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UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  NO.  256 


PHYLLOSTICTA  LEAF  SPOT,  FRUIT  BLOTCH, 

AND  CANKER  OF  THE  APPLE:    ITS 

ETIOLOGY  AND  CONTROL 

By  EMIL  FREDERICK  GUBA 


CONTENTS  OP  BULLETIN  No.  256 

PAGE 

THE  DISEASE   481 

Names  Applied  481 

Historical   481 

Probable  Origin 484 

Distribution  and  Prevalence  in  Illinois 485 

Plants  Affected    487 

ETIOLOGY 488 

Morphology  of  the  Pathogene 488 

Pycnidia  488 

Pycnospores   > '. 490 

Conidiophores 491 

Mycelium 491 

Nomenclature 492 

Physiology   494 

Cultural  Characters   494 

Factors  Involved  in  Growth  and  Pycnosclerotia  Formation 496 

Spore  Production  in  Culture 498 

Spore  Germination   500 

Life  History   505 

Inoculation  and  Infection 505 

Sources  of  Inoculum 506 

Time  of  Infection 507 

Conditions  Associated  with  Natural  Infection 517 

Development  of  the  Fungus 519 

Varietal   Susceptibility   526 

Dissemination 528 

CONTROL  MEASURES 530 

Historical :    Methods  That  Have  Been  Advocated 530 

Dormant  Spraying   533 

Experiments  with  Dormant  Sprays 535 

Effect  of  the  Fungicide 539 

Experiments  with  Summer  Sprays 541 

Summer  Spraying :    Conclusions 548 

Other  Aspects  of  Control 550 

Soil  Treatments   550 

Pruning 550 

Surgery 551 

Protective  and  Preventive  Measures 551 

Selection  and  Location  of  Varieties 552 

Recommendations  for  Control 552 

LITERATURE  CITED    .                                                                                          .  554 


PHYLLOSTICTA  LEAF  SPOT,  FRUIT  BLOTCH, 

AND  CANKER  OF  THE  APPLE:   ITS 

ETIOLOGY  AND  CONTROL1 

BY  EMIL  FREDERICK  GUBAb 

The  increasing  prevalence  and  seriousness  of  apple  blotch  in  Illinois 
and  thruout  the  United  States,  and  the  inadequacy  of  present  control 
measures  emphasize  the  need  of  detailed  study  of  the  life  history 
and  habits  of  the  causal  organism,  Phyllosticta  solitaria  E.  &  E.  Since 
the  first  published  account  of  the  disease  on  the  commercial  apple  in 
1902,  valuable  observations  and  isolated  facts  have  been  presented  by 
many  investigators.  Existing  publications  on  the  disease,  however, 
show  a  lack  of  knowledge  of  many  important  phases  of  nje  organism 
necessary  for  its  successful  control. 

THE  DISEASE 
NAMES  APPLIED 

Before  anything  definite  was  known  about  apple  blotch,  fruit 
growers  regarded  it  as  an  unusual  stage  of  apple  scab  or  apple  bitter 
rot.  Up  to  1907,  the  disease  was  known  variously  as  "apple  blotch," 
' '  fruit  blotch, "  ' '  dry  rot, "  '  <  black  scab, ""  late  scab, "  "  cancer, "  ' '  tar 
blotch,"  "Phyllosticta,"  ' ' Phyllostictose, "  "star  fungus,"  "Phyllos- 
ticta  spot,"  or  ' ' Phyllosticta  on  the  apple."  As  more  was  known 
about  the  disease  it  came  generally  to  be  referred  to  as  apple  blotch, 
and  this  is  the  name  that  will  be  used  in  this  bulletin. 


HISTORICAL 

*£*'  £$> 

Specimens  of  fhe  disease  were  first  collected  in  October,  1893,  by 
L.  M.  Underwood92  on  the  leaves  of  the  American  crab  apple  (Pyrus 
coronaria  L.)  in  Montgomery  county,  Indiana.  They  were  submitted 
for  examination  to  J.  B.  Ellis,  who  determined  the  causal  organism 
to  be  a  Phyllosticta,  to  which  he  gave  the  name  Phyllosticta  solitaria; 
in  1895,  he  furnished  a  meagre  description  of  it.  A  few  months  pre- 
vious to  the  publication  of  the  description  of  Phyllosticta  solitaria,  by 
Ellis  and  Everhart,30  M.  B.  Waite,  pathologist  of  the  Bureau  of  Plant 
Industry,  U.  S.  Department  of  Agriculture,  photographed  blotched 


aThe  results  presented  in  this  bulletin  form  part  of  a  thesis  submitted  by 
the  author  to  the  Graduate  School  of  the  University  of  Illinois  in  partial  fulfilment 
of  the  requirements  for  the  degree  of  doctor  of  philosophy  in  botany,  May,  1923. 
The  writer  wishes  to  express  to  Dr.  H.  W.  Anderson,  Assistant  Chief  in  Pomol- 
ogical  Pathology  in  Horticulture,  and  to  Dr.  F.  L.  Stevens,  Professor  of  Plant 
Pathology  in  Botany,  his  appreciation  for  their  supervision  of  the  study  and  for 
their  suggestions  and  criticisms  in  the  preparation  of  the  manuscript.  He  is 
indebted  to  Dr.  C.  F.  Hottes,  Professor  of  Plant  Physiology  in  Botany,  for  the 
use  of  his  laboratory  and  for  suggestions  in  the  study  of  the  temperature  rela- 
tions of  the  fungus  in  culture,  and  to  others  who  have  shown  interest  in  the  work. 

b  Formerly  Assistant  in  Pomology  and  Fellow  in  Botany  in  the  Graduate 
School. 

481 


482 


BULLETIN   No.   256 


[February, 


fruits  of  Malus  Mains  L.  collected  from  localities  about  Washington, 
D.  C.,  and  identified  the  causal  organism  as  a  species  of  Phyllosticta 
(Fig.  1).  Owing  to  the  uncertainty  which  existed  at  that  time  con- 
cerning the  causal  agent  of  the  frog-eye  apple  leaf  spot,  Waite  sup- 
posed that  the  fruit  blotch  and  the  frog-eye  leaf  spot  were  the  results 
of  the  same  organism,  but  was  in  no  way  certain  of  his  hypothesis.  So 


FIG.  1. — APPLE  BLOTCH 

Specimens  collected  at  Garrett  Park,  Montgomery  county, 
Maryland,  by  M.  B.  Waite;  (A)  1897,  (B)  1895  (photographs  by 
M.  B.  Waite). 

many  Phyllostictas  on  the  apple  were  then  known  that  he  was  un- 
willing to  make  any  statement  as  to  the  causal  fungus  further  than 
that  it  was  a  species  of  Phyllosticta.*  In  1902  Clinton17  gave  the  first 
published  account  of  the  disease  on  the  commercial  apple  and  called 
attention  to  its  prevalence  in  the  apple  regions  of  southern  Illinois. 
Clinton  cultured  the  organism  and  described  its  microscopic  char- 
acters. He  considered  the  fungus  a  new  species  of  the  genus  Phyllos- 


•Information  obtained   from  personal  correspondence.     These  collections  by 
M.  B.  Waite  represent  the  earliest  record  of  apple  blotch  on  the  commercial  apple. 


APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  483 

ticta.  At  about  the  same  time  Faurot31  of  Missouri  had  his  attention 
called  to  the  disease  by  growers  who  had  mistaken  it  for  a  dormant 
condition  of  bitter  rot. 

What  appear  to  be  the  first  experiments  involving  the  control  of 
apple  blotch  were  conducted  in  1903  by  C.  S.  Crandall23  of  the  Illinois 
Agricultural  Experiment  Station  in  the  investigation  of  the  compara- 
tive efficiency  of  Bordeaux  dust  and  liquid  Bordeaux  in  the  control  of 
apple  insects  and  diseases.  The  first  investigation  directed  primarily 
toward  the  control  of  apple  blotch  was  conducted  by  Scott  and  Quaint- 
ance77  in  1906  in  Benton  county,  Arkansas.  Their  spraying  experi- 
ments resulted  in  the  use  of  a  spray  schedule,  which  at  that  time  gave 
satisfactory  control  of  the  disease. 

To  Sheldon86  we  are  indebted  for  knowledge  of  the  fact  that 
Phyllosticta  solitaria  E.  &  E.  on  the  leaves  of  Pyrus  coronaria  is  iden- 
tical with  the  organism  producing  the  bark  canker,  leaf  spot,  and  the 
fruit  blotch  of  the  commercial  apple.  Sheldon  did  not  attempt  cross 
inoculations,  and  type  specimens  of  the  fungus  were  not  examined. 
His  conclusions,  however,  were  generally  accepted. 

At  the  same  time  Scott  and  Rorer,78  at  Bentonville,  Arkansas, 
established  by  isolation  of  the  fungus,  comparison  of  its  growth  in 
culture,  and  by  inoculation  of  the  host  with  spores  from  natural 
sources,  the  identity  of  the  organism  causing  the  bark  canker,  leaf 
spot,  and  fruit  blotch  of  the  apple. 

Stevens 87>  88  in  1907  found  blotch  for  the  first  time  in  North  Caro- 
lina. In  1908  Garman37  reported  it  in  Kentucky,  Morris  and  Nichol- 
son52 cited  its  prevalence  and  seriousness  in  Oklahoma,  and  Orton  and 
Ames56' 57  reported  its  general  distribution  in  the  region  extending 
from  Maryland  and  the  Carolinas  to  Arkansas  and  Missouri.  Doug- 
lass26 in  1909  and  McCormack53  in  1910  reported  its  prevalence  in 
southern  Indiana,  and  in  1910  Selby82  and  Gloyer39  recorded  it  for 
Ohio ;  Orton8  found  it  in  Pennsylvania,  and  Beach*  in  South  Dakota. 
As  early  as  1912,  according  to  Cook,22  apple  blotch  was  common  in 
New  Jersey. 

Scott  and  Rorer79  in  the  period  19Q6  to  1909  conducted  the  first 
general  study  of  the  apple  blotch  fungus.  Their  study  dealt  briefly 
with  the  etiology  of  the  disease,  the  cultural  and  morphological  char- 
acters of  the  fungus,  its  life  history,  and  control. 

Since  1912  some  attention  has  been  directed  to  the  control  of 
apple  blotch  with  dormant  sprays.  Such  a  possibility  was  originally 
conceived  by  growers  in  Illinois,  was  first  given  experimental  atten- 
tion by  Watkins106' 107  of  Illinois,  and  later  was  taken  up  on  several 
occasions  by  the  Agricultural  Experiment  Stations  in  Illinois  and 
Indiana. 


•Information  obtained  by  personal  correspondence. 


484  BULLETIN   No.   256  [February, 

Lewis51  in  1913  presented  an  extensive  account  of  apple  blotch 
embodying  descriptions  of  the  disease  on  various  varieties  of  apples 
and  the  results  of  his  experiments  in  its  control. 

Since  the  publication  of  the  paper  by  Scott  and  Korer,79  experi- 
mental work  on  blotch  control  has  been  concerned  particularly  with 
the  relative  merits  of  Bordeaux  and  lime  sulfur,  and  the  time  of  the 
applications.  In  connection  with  this  experimental  work  the  results  of 
Lewis,51  Blair  et  al.,8  Gunderson,42'45  Cooper,20  Roberts,67'69  Beach,5'7 
Brock,9-  «• 13'15  and  Selby82- 83  should  be  noted.  The  results  of  Beach5'7 
demonstrated  the  value  of  a  spray  two  weeks  after  petal  fall,  supple- 
mentary to  applications  recommended  by  previous  investigators.  The 
probability  of  primary  infection  earlier  than  three  weeks  after  petal 
fall  had  been  suggested  previously  by  Lewis51  of  Kansas,  Cooper20  of 
Nebraska,  Rolfs71' 72  of  Oklahoma,  Brock13  of  Illinois,  and  Stover  et 
al.90  of  Ohio. 

In  1917  Roberts67  confirmed  the  previous  inoculation  work  of 
Scott  and  Rorer  by  successfully  inoculating  the  host  with  spores  from 
pure  culture.  In  1921  Roberts68  demonstrated  by  artificial  inocula- 
tion that  only  the  current  season's  growth  is  susceptible  to  blotch 
infection. 

In  1920  Anderson3  reported  the  distribution  of  the  disease  in 
Illinois  and  outlined  a  plan  embodying  exclusion,  prevention,  quar- 
antine, and  inspection  measures,  whereby  he  believed  it  possible  to 
restrict  the  disease  to  its  confines  in  Illinois  at  that  time,  and  thus 
prevent  its  northward  migration. 

In  1922  Gardner35  of  Indiana  found  that  most  of  the  apple  blotch 
cankers  are  the  direct  result  of  petiole  and  bud  scale  infections.  He 
reported  that  the  mycelium  from  the  basal  petiole  lesions  crosses  the 
absciss  layer  before  leaf  fall,  invades  the  bark  and  produces  a  canker 
about  the  bud  which,  in  the  majority  of  cases,  becomes  conspicuous 
the  following  spring.  Lewis,51  and  Scott  and  Rorer78  observed  that 
cankers  originated  in  this  manner,  but  the  seriousness  of  this  method 
of  infection  was  emphasized  by  Gardner. 

In  1923  Gardner  and  Jackson36  suggested  surgical  measures  to 
eradicate  cankers  from  young  apple  stock  and  thus  avoid  an  increase 
of  new  cankers  in  young  orchards. 

The  timely  reports  of  the  Plant  Disease  Survey,  U.  S.  Department 
of  Agriculture,93'102  from  1917  to  the  present,  have  been  exceedingly 
valuable  as  a  source  of  information  on  the  annual  prevalence,  distri- 
bution, and  losses  from  this  disease. 

PROBABLE  ORIGIN 

Collections  of  apple  blotch  from  widely  scattered  localities  (see 
page  481)  prior  to  1902  establish  the  proof  of  the  wide  distribution  of 


1925} 


APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL 


485 


the  fungus  even  at  that  early  period  and  support  the  contention  that 
the  disease  did  not  arise  locally  on  the  commercial  apple. 

The  original  host  of  this  fungus  was  probably  the  native  crab 
apple  (Pyrus  coronaria}  and  during  the  past  few  years  in  Illinois 
and  Indiana  the  fungus  often  has  been  found  on  this  host.  Sheldon86 
found  it  on  this  species  of  native  crab  apple  in  West  Virginia,  and 
Scott  and  Rorer79  in  Pennsylvania.  The  fungus  still  exists  in  a  severe 
form  on  this  host,  but  in  a  less  serious  degree  than  on  susceptible  vari- 
eties of  commercial  apples.  This  may  be  explained  thru  the  fact  that 


FIG.  2. — DISTRIBUTION  OF  APPLE  BLOTCH  IN  THE  UNITED  STATES, 
1916-1923 


the  native  crab  may  have  gradually  developed  partial  immunity  dur- 
ing its  long  period  of  susceptibility  in  its  native  habitat.  With  the 
rise  and  development  of  commercial  fruit  growing  in  the  eastern  half 
of  the  United  States,  the  extensive  planting  of  -varieties  susceptible  to 
the  apple  blotch  fungus,  and  favorable  climatic  conditions,  the  fungus 
adapted  itself  to  growth  on  the  commercial  apple  and  developed  into 
a  serious  disease  producer. 

The  disease  first  became  seriously  destructive  in  the  Ozark  apple 
region.  During  the  period  1900  to  1902  in  southern  Illinois,  Arkansas, 
and  southern  Missouri  it  was  generally  prevalent  and  serious.  In  the 
time  which  has  since  elapsed  it  has  spread  over  most  of  the  eastern 
half  of  the  United  States  (Fig.  2). 


DISTRIBUTION  AND  PREVALENCE  IN  ILLINOIS 

•Clinton17  stated  that  apple  blotch  was  found  in  a  number  of  places 
in  southern  Illinois  by  Burrill  in  1901 ;   that  growers  were  aware  of 


486  BULLETIN   No.   256  [February, 

its  presence  earlier,  and  that  it  was  present  in  an  orchard  at  Dubois, 
Washington  county,  for  some  time  previous  to  1901.  Since  its  first 
reported  appearance,  it  has  developed  into  epidemic  form  in  the  cen- 
ters of  apple  production. 

No  information  is  available  to  show  the  periodic  progress  of  the 
disease  northward.  Crandall,23  in  19'03,  found  apple  blotch  prevalent 
on  Ben  Davis  trees  south  of  Olney,  in  Richland  county,  and  in  1912 
Ruth8  reported  infection  of  approximately  70  percent  of  the  apples 
on  unsprayed  Ben  Davis  and  Jonathan  trees  in  an  orchard  at  Flora. 

The  accounts  of  the  spraying  experiments  of  Crandall23  in  1904, 
and  of  Foglesong32  in  1909  at  Griggsville,  Pike  county,  do  not  include 
data  on  apple  blotch.  Likewise,  the  absence  of  any  statements  con- 
cerning apple  blotch  in  the  accounts  of  the  spraying  experiments  of 
Gunderson8  in  Ben  Davis  orchards  in  Pike  county  in  1911  and  1912. 
indicates  that  apple  blotch  was  not  present  or  at  least  was  not  serious 
in  southwestern  Illinois  in  this  period. 

The  account  of  the  spraying  experiments  of  Watkins8  with  fifteen- 
year-old  Ben  Davis  trees  at  Neoga,  Cumberland  county,  for  three 
seasons,  1910  to  1912,  does  not  mention  apple  blotch.  Blotch,  evi- 
dently, was  not  present  in  the  orchard  and  very  likely  not  established 
in  the  vicinity. 

With  the  meager  information  available,  together  with  a  knowledge 
of  the  development  of  fruit  growing  in  Illinois,  it  seems  probable  that 
the  fungus  came  into  Illinois  from  the  apple-growing  region  to  the 
southwest,  and  that  the  disease  appeared  at  about  the  same  time  in  all 
of  southern  Illinois  coincident  with  the  extensive  development  of  the 
apple  industry.  The  Pike-Calhoun  apple  section,  being  of  recent  de- 
velopment and  with  different  conditions,  remained  relatively  free  of 
blotch  until  1913. 

Knowledge  of  the  disease  in  central  Illinois  is  limited  to  recent 
years.  Evidence  points  to  the  appearance  of  the  disease  on  North- 
western Greening  in  the  University  orchards,  Champaign  county,  in 
1917.  It  appeared  at  about  the  same  time  on  Northwestern  Greening 
at  Lilly,  Tazewell  county,  at  Yates  City,  Knox  county,  and  near  Dan- 
ville, Vermilion  county.  At  Lilly  the  disease  may  also  be  traced  to 
infections  of  1917  on  Ben  Davis,  Missouri  Pippin,  and  Duchess  vari- 
eties. In  1921,  in  the  Lilly  orchards,  90  percent  of  the  fruit  of  North- 
western Greening  trees  was  affected  with  blotch,  which  indicates  that 
epidemic  development  of  the  disease  after  its  first  appearance  at  Lilly 
was  but  a  matter  of  a  few  years. 

In  1920  the  disease  was  found  on  Red  Astrachan  in  Peoria  county, 
on  Northwestern  Greening  and  Duchess  in  Ogle  county,  and  on 
Duchess  in  Kendall  county.  In  Ogle  and  Kendall  counties  the  epi- 
demic development  of  blotch  on  Duchess  trees  in  a  home  orchard  lends 


WSS5}  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  487 

support  to  the  belief  that  the  disease  may  have  been  present  since 
1917-1918.  In  1921  the  prevalence  of  apple  blotch  was  observed  on 
Northwestern  Greening  at  Eome,  Peoria  county.  In  the  same  year 
a  trace  of  it  was  found  on  the  same  variety  near  Galena,  Jo  Daviess 
county.  The  appearance  of  this  disease  in  isolated  regions  in  central 
and  northern  Illinois  within  the  last  few  years  suggests  that  its  dis- 
tribution in  this  region  is  comparatively  recent. 

Apple  blotch  to-day  is  present  thruout  Illinois.  South  of  the  40th 
parallel,  i.e.,  south  of  the  tier  of  counties  extending  east  and  west 
approximately  from  Adams  to  Vermilion  counties,  it  is  very  preva- 
lent and  is  a  limiting  factor  in  the  commercial  production  of  sus- 
ceptible varieties  of  apples.  In  the  Pike-Calhoun  apple  section, 
however,  the  disease  is  generally  much  less  severe  and  less  prevalent 
than  in  the  more  central  and  southern  sections  of  this  area.  In  the 
area  of  the  41st  parallel,  i.e.,  extending  east  of  Henderson,  Hancock, 
and  the  northern  half  of  Adams  counties,  apple  blotch  is  now  rather 
generally  present  and  well  established  on  Duchess  and  Northwestern 
Greening  and  is  rapidly  passing  to  other  less  susceptible  varieties. 
Its  progress  in  this  section  has  been  comparatively  slow  in  the  absence 
of  extensive  plantings. 

In  northern  Illinois  apple  blotch  is  local  and  found  only  in  scattered 
places.  Severe  cases  of  it  have  been  found  in  home  orchards,  where 
spraying  and  the  culture  of  the  apple  often  are  neglected. 

PLANTS  AFFECTED 

Apple  blotch  is  strictly  a  disease  of  certain  species  of  the  genus 
Malus  of  Hall.  The  disease  has  never  been  found  on  any  other  host, 
altho  recently  Seaver81  has  named  Crataegus  sp.  as  a  host  for  the 
fungus. 

The  confusion  existing  in  the  nomenclature  of  our  native  mid- 
western  crab  apples  renders  an  accurate  designation  of  the  susceptible 
species  difficult.  In  Illinois,  Malus  lancifolia  Eehd.  and  Malus  coro- 
naria  L.  are  very  susceptible  and  Malus  angustifolia  Michx.  is  mod- 
erately so.  The  disease  has  been  found  occasionally  on  Malus  angusti- 
folia in  Union  county,  and  on  Malus  lancifolia  and  Malus  coronaria 
in  central  Illinois  and  central  Indiana.  The  common  prairie  crab 
apple  (Malus  ioensis  Britt.)  and  its  varieties  are  resistant;  the  dis- 
ease never  has  been  found  on  them.- 


488  BULLETIN  No.   256  [February, 


ETIOLOGY 

MORPHOLOGY  OF  THE  PATHOGENE 
Pycnidia 

The  pycnidia  vary  in  size  and  form  according  to  the  organs  of  the 
plant  affected.  They  are  smallest  on  the  leaf  spots,  being  globose  or 
sub-globose  and  with  a  thin  wall.  On  the  petioles  they  are  similar 
in  form,  but  somewhat  larger.  On  the  fruit  they  are  considerably 
depressed  and  elliptical,  with  thick  lateral  walls.  On  the  bark  they 
are  very  large  and  the  carbonaceous  walls  are  more  extensively  de- 
veloped than  elsewhere. 

On  the  leaf  spots  the  pycnidia  have  a  small,  Tostrate  ostiole  which 
measures  9  to  12/x  long  and  7  to  12/*  wide  (Plate  1,  Fig.  H,  I).  The 
pycnidia  vary  in  diameter  from  60  to  95/x.  The  pycnidial  wall  is 
comparatively  thin,  generally1  consisting  of  one  or  two  layers  of  dark- 
colored  cells  and  measures  6  to  7/t  wide.  The  wall  is  much  thicker 
at  the  top  and  after  the  formation  of  the  ostiole  the  thickened  wall 
is  retained  around  the  short  neck.  Next  to  the  wall  within  are  the 
narrow  sporogenous  layers  of  hyaline  parenchyma  cells  bearing 
conidiophores. 

The  pycnidia  on  the  petioles  are  commonly  larger  than  those 
formed  on  the  leaf  spots  and  measure  62  to  119/x,  in  diameter,  and 
have  a  definite,  thin,  dark-colored,  and  regular  wall  (Plate  1,  Figs.  D, 
G,  J).  About  the  ostiole  the  walls  are  broader  and  the  cells  are 
denser  than  at  the  sides  and  base  of  the  pycnidium.  The  beak  meas- 
ures 12  to  14/x  long  and  9  to  12u  wide.  Within  the  narrow  dark-col- 
ored wall  the  larger  hyaline  sporogenous  cells  with  conidiophores  ap- 
pear in  sharp  contrast. 

On  the  fruit  the  pycnidia  are  black,  punctiform,  and  prominent 
(Plate  1,  Figs.  E,  F).  They  may  be  aggregated  and  fused,  but  usually 
their  individuality  is  retained.  They  are  decidedly  depressed  or 
elliptical  and  almost  twice  as  wide  as  deep.  The  lateral  walls  are  14  to 
16/u,  thick  and  the  basal  wall  is  about  4.75/t  thick.  The  ostiole  is  in- 
definite, without  a  neck,  and  usually  the  wall  around  it  is  as  broad  as 
the  lateral  walls.  The  diameter  of  the  stoma  varies  from  12  to  23/*. 
The  wall  is  regular  and  definite,  and  adjoining  it  within  are  the  hyaline 
cells  of  the  thin  sporogenous  layer.  The  pycnidia  on  the  fruit  vary 
in  size,  from  57  to  95/*  deep  and  107  to  166/x  wide.  Upon  the  dis- 
charge of  spores  in  summer  the  sporogenous  tissue  lining  the  interior 
of  the  pycnidium  is  rejuvenated  and  eventually  fills  the  entire  cavity 
while  the  ostiole  is  closed  by  the  growth  of  the  wall  cells.  During 
the  fall  and  winter  months  the  interior  is  occupied  by  pseudo-paren- 


PLATE  I.— SECTIONS  THRU  PYCNIDIA  OF  P.  solitaria,  SHOWING  THE  VARIATION  IN 

SIZE  AND  FORM 

(A,  B)  From  bark  cankers,  the  original  pycnosclerotia ;  (C)  from  the  ad- 
vancing area  of  the  canker  formed  in  the  spring;  (D,  G,  J)  from  petioles: 
(E,  F)  from  the  fruit  in  June  and  July;  (H,  I)  from  the  leaf  blades. 


1925] 


APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL 


489 


chyma  tissue  enclosed  in  a  thick  carbonaceous  wall.  Extensive  en- 
largement of  the  pycnidium  occurs  and  often  results  in  the  fusion  of 
the  pycnidia.  Such  fruits  with  dense,  thick,  carbonaceous  walls,  en- 
closing a  hyaline  parenchyma  context  have  been  named  pycnosclerotia 
(Fig.  3)  by  Eeddick.66- " 

On  the  bark  two  types  of  fruiting  bodies  are  recognized :  first,  the 
pycnidia  which  form  and  function  in  the  same  season;  and  second, 
the  pycnosclerotia  which  form  in  the  late  summer,  pass  the  winter 
in  a  dormant  condition,  and  function  the  following  spring  (Plate  1, 
Figs.  A,  B,  C,  and  Fig. 
3).  Both  forms  at  first 
resemble  the  pycnidia  on 
the  fruit  in  form  and 
shape ;  depressed,  wider 
than  long,  and  with  thick 
lateral  and  thin  basal 
walls.  The  pycnidia  usu- 
ally develop  a  distinct 
ostiole  and  the  thickness 
of  the  wall  is  more  or 
less  limited.  In  pycnos- 
clerotia, the  ostiole  is 
usually  indefinite  and  re- 
sults from  the  rupture 
and  removal  of  a  part 
of  the  thick  protective 
apical  wall. 

Pycnosclerotia  formed 
in  late  summer  are  in 
the  following  spring 

comparatively  large,  with  thick,  carbonaceous  walls  and  without  a 
definite  ostiole.  Spore  formation  commences  in  the  center  of  the 
pseudo-parenchyma  early  in  the  year  and  the  sporogenous  layer  which 
is  formed  gradually  progresses  outward.  When  sporulation  is  complete 
only  the  dark  wall  cells  remain,  enclosing  the  spores.  Apically  and 
laterally  the  walls  are  broader  than  at  the  base.  The  apical  wall 
measures  from  23  to  48/i  thick ;  the  lateral  wall  from  35  to  47/*,  and 
the  basal  wall  from  7  to  28/x.  The  pycnosclerotia  are  globose  or  sub- 


FIG.  3. — SECTION  THRU  A  PYCNOSCLEROTIUM  OF 

P.  solitaria  FROM  A  CANKER  COLLECTED 

IN  DECEMBER 

Note  the  dense,  carbonaceous  wall  and  the 
hyaline  interior  parenchyma  context. 


*  Eeddick  first  used  the  term  pycnosclerotium  referring  to  a  pycnidium  with 
a  thick  carbonaceous  wall  enclosing  a  pseudo-parenchyma  context  of  large  hyaline 
cells  which  gives  rise  to  a  perithecium.  Since  perithecia  have  never  been  found  to 
result  from  the  differentiation  of  the  pycnosclerotium  of  P.  solitaria,  the  word  is 
here  used  in  a  slightly  different  sense  from  that  of  Reddick,  altho  the  form  and 
structure  of  the  fruit  is  in  all  respects  the  same. 


490 


BULLETIN   No.   256 


[February, 


globose.    The  ostiole  measures  from  23  to  59/x  wide.    The  pycnosclerotia 
measure  155  to  274/x,  wide  and  107  to  238/u,  deep. 

Pycnospores 

The  pycnospores  are  ovoid  or  broad-elliptic,  unicellular,  hyaline, 
multi-guttulate,  with  a  smooth  wall  which  occasionally  is  partly  cov- 
ered at  the  broad  end  by  an  elongated,  gelatinous  appendage  (Figs. 
4,  9 A1).  The  guttules  are  ordinarily  uniform  in  size  and  form  and 
evenly  distributed  in  the  cell  tho  often  they  are  fused  to  form  broad. 

greenish,  irregular  bands.  In 
immature  spores  commonly 
one  large  guttule  may  almost 
fill  the  entire  spore  cell.  The 
spores  range  in  size  from  7 
to  11/u,  long  and  6  to  8.5ju,  wide. 
The  spores  of  Phyllosticta 
solitaria  from  the  pycnos- 
clerotia bear  a  gelatinous, 
hyaline  appendage  which  is  at 
first  very  long  and  narrow, 
and  considerably  broadened 
at  the  base.  It  envelops  about 
one-half  of  the  spore  at  the 
broad  end.  The  appendage 
may  appear  as  a  thick  cap 
over  the  broad  pole  of  the 
spore.  This  gelatinous  cap  or 
appendage  has  never  been 
observed  on  spores  from 
pycnidia  which  form  and 
function  in  the  same  season ; 
however,  it  is  constant  on  the 
spores  in  the  pycnosclerotia  in  the  host  and  in  artificial  culture. 

Other  Phyllostictas  show  morphological  characters  similar  to  those 
of  Phyllosticta  solitaria,  e.  g.,  the  imperfect  forms  of  Guignardia 
bidwellii  (E)  V.  &  R.  and  Guignardia  vaccinii  Shear.  Shear84  in  the 
study  of  the  above  forms  noted  the  gelatinous  appendage  on  the  spores 
of  Guignardia  bidivettii.  He  described  and  figured  similar  append- 
ages on  the  imperfect  spores  of  Guignardia  vaccinii. 

Stewart89  has  described  and  illustrated  similar  appendages  on  the 
imperfect  spore  form  of  Guignardia  aesculi  (Pk.)  Stewart.  These 
descriptions  agree  with  the  character  of  the  appendages  on  the  spores 


FIG.  4. — SPORES  OP  P.  solitaria  FROM  PURE 
CULTURE 


1925]  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  491 

of  P.  solitaria  from  pure  culture  and  from  the  pycnosclerotia  in  the 
host  cankers. 

ConidiopJiores 

The  conidiophores  arise  from  a  hyaline  sporogenous  layer  of  cells 
which  is  supported  by  a  colorless  pseudo-parenchymatous  sheath  lin- 
ing the  dark  wall  of  the  pycnidium  (Plate  2).  Sometimes  the  pycni- 
dial  membrane  is  not  sharply  limited,  but  appears  gradually  to  dif- 
ferentiate, on  the  interior,  into  hyaline  pseudo-parenchyma  tissue. 


A 

FIG.  5. — MYCELIUM  OP  P.  solitaria  FROM  PURE  CULTURE 
(A)  From  margin  of  a  young  colony,  (B)  from  an  old  culture. 

This  tissue  does  not  react  readily  with  common  stains  and  appears 
more  or  less  hyaline  and  somewhat  obscure  in  stained  sections. 

The  sporogenous  layer  is  composed  of  very  small  and  narrow  cells 
from  which  the  conidiophores  arise.  The  conidiophores  are  simple, 
unicellular,  excepting  in  the  pycnosclerotia,  where  in  the  early  stages 
of  differentiation  they  are  long  and  septate.  They  may  be  filiform, 
long,  obclavate,  and  irregularly  curved  or  straight;  or  they  may  be 
short,  broad,  straight,  columnar,  and  almost  as  wide  as  the  supported 
spore.  They  usually  measure  from  4  to  11/u,  long  and  1  to  3ju,  wide. 
Commonly  they  taper,  being  broader  at  the  base  than  at  the  apex. 

Mycelium 

The  mycelium  in  culture  is  composed  of  septate,  pale  green  hyphac 
which  branch  irregularly.  The  mode  of  branching,  the  irregular  form, 
size,  and  the  bulging  of  the  cell  walls  are  very  characteristic. 

The  young,  long,  slender,  and  actively-growing  hyphae  measure 
about  2  to  3^,  in  diameter;  septa  are  rare  and  the  walls  are  not  con- 
stricted (Fig.  5,  A).  Occasional  bulging  lateral  walls  mark  the  begin- 
ning of  new  filaments.  Anastomosis  is  frequent  along  the  walls. 
Transversely  in  the  cells  there  are  definite,  rather  large,  irregularly- 
shaped,  colorless  vacuoles  and  bands  of  a  pale  olivine  substance.  The 


492  BULLETIN   No.   256  [February, 

color  of  the  young  colonies  in  culture  is  due  probably  to  a  colored 
pigment  in  the  globules  and  bands  of  the  substance  along  the  walls 
and  across  the  cells. 

In  the  old  mycelium  the  cells  are  short  and  thick,  6  to  8/*  wide  and 
occupied  by  large  globules  of  a  greenish  color;  septation  is  frequent 
and  the  walls  are  prominently  constricted  at  the  septa  and  at  the 
bases  of  the  short,  stout  branches  that  arise  at  irregular  angles  (Fig. 
5,  B).  The  anastomosis  of  these  stout  cells  produces  a  very  irregular 
network. 

NOMENCLATURE 

The  original  description  of  Phyllosticta  solitaria  was  published 
by  Ellis  and  Everhart30  in  1895,  as  follows: 

"Phyllosticta  solitaris  E.  &  E.  On  leaves  of  Pyrus  eoronarw,  Crawfordsville, 
la.,  Oct.,  1893.  Prof.  L.  M.  Underwood.  Spots  minute,  1  millimeter,  round 
pale-white,  with  a  darker  border.  Perithecia  epiphyllous,  solitary,  one  in  the 
center  of  each  spot,  75/x  diameter.  Sporules  sub-globose,  hyaline,  nudeate,  5  to  6/t 
diameter. '  * 

The  locality  of  this  collection  has  been  misrepresented  by  many. 
Sacearado74  refers  to  the  collection  from  "Iowa,  Amer.,  bor.,"  but  this 
misrepresentation  is  due  to  Ellis'  incorrect  abbreviation  of  Indiana, 
namely  "la."  on  the  original  packet.  Saccardo  changed  the  ending 
of  the  specific  name  "solitaris"  to  "solitaria,"  since  the  gender  of 
Phyllosticta,  by  common  usage,  is  feminine. 

Type  specimens  of  the  fungus  were  not  available  for  personal 
study.  Thru  the  kindness  of  Professor  H.  M.  Fitzpatrick,  the 
specimen  in  the  Everhart  herbarium  (Vol.  2,  p.  57)  at  Harvard  Uni- 
versity was  examined  and  compared  with  specimens  of  the  fungus 
on  apple  foliage  from  Illinois.  He  writes,  "I  feel  no  hesitancy  in 
saying  that  your  material  agrees  with  the  type  in  external  appear- 
ance. ' '  Scott  and  Rorer79  examined  the  type  specimen  of  Phyllosticta 
solitaria  from  the  New  York  Botanical  Gardens  and  found  that  the 
spores  were  identical  with  those  of  the  apple  blotch  fungus. 

The  genera  Phoma  and  Phyllosticta  are  very  large,  the  former 
comprizing  approximately  1,700  form-species  and  the  latter  more  than 
1,100  form-species.  Allescher2  calls  attention  to  certain  differences 
between  these  genera,  such  as  the  small,  sometimes  indistinct  papilla, 
and  filiform,  sometimes  short  or  indistinct  conidiophores  in  Phoma, 
and  the  relative  absence  of  the  small  papilla,  and  the  very  short,  rarely 
distinctly  developed  or  absent  conidiophores  in  Phyllosticta.  They  are 
further  segregated  in  that  Phyllosticta  is  only  leaf-inhabiting  while 
Phoma  occurs  on  branches,  twigs,  stems,  pedicels,  petioles,  and  on 
the  needles  of  the  conifers.  In  practice  it  is  customary  to  regard  a 
species  as  a  Phyllosticta  if  on  the  leaves,  and  as  a  Phoma  if  on  the 
stems.  This  artificial  classification  is  unsatisfactory  and  worthless. 


PLATE  2. — SECTIONS  THRU  PYCNIDIA  FROM  DIFFERENT  ORGANS  OF  THE  HOST 
SHOWING  THE  SPOROGENOUS  LAYER 

(A)   From  the  leaves  (blades)  ;    (B)  from  the  petioles;    (C)  from  the  fruit; 
(D)   from  the  advancing  area  of  the  canker. 


1925]  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  493 

It  is  evident  that  the  species  at  present  in  the  genera  Phoma  and 
Phyllosticta  should  be  critically  examined  in  order  to  segregate  them 
into  several  genera  on  morphological  grounds. 

In  1916  Sydow91  created  the  genus  Phyllostictina  based  on  the 
type  Phyllostictina  murrayae  Syd.,  occurring  on  living  leaves  of 
Murrayae  koenigii,  from  Dehra  Dun,  India. 

Von  Hohnel48  later  studied  the  type  specimen  of  Phyllostictina 
murrayae  Syd.,  and  contends  that  its  characters  closely  agree  with 
those  of  Phoma  uvicola  B.  &  C.,  and  comments  that  he  found  no  trace 
of  conidiophores  altho  he  assumes  that  they  were  originally  present 
and  had  dissolved.  He  claims  that  both  of  these  fungi  belong  to 
the  same  form  genus  and  to  receive  them  he  emends  the  description 
of  the  genus  Phyllostictina. 

Professor  Sydow  furnished  the  writer  with  type  specimens  of 
Phyllostictina  murrayae  for  study.  The  outstanding  characters  are 
the  globose  pycnidia  with  dark  brown,  thin  parenchyma-like  walls 
composed  of  two  layers  of  thin-walled  cells,  with  usually  a  definite 
ostiole  surrounded  by  a  slightly  thickened  ring  of  wall  cells.  The 
spores  are  ovate,  or  broadly  elliptical,  and  contain  numerous,  uniform 
round  globules.  From  microtome  sections  of  the  specimen  these  spores 
appear  to  be  formed  by  the  histolysis  of  the  gelatinous  parenchyma- 
tous  context,  without  conidiophores. 

Phyllosticta  solitaria  is  certainly  not  a  typical  Phyllosticta  and 
also  cannot  be  regarded  as  a  Phyllostictina  since  it  does  not  agree  with 
the  type  nor  with  the  original  description  altho  it  does  agree  with 
the  emended  description  of  von  Hohnel.  It  is  evident  that  von 
Hohnel 's  emended  description  is  applicable  to  Phoma  uvicola  and  to 
Phyllosticta  solitaria  but  not  to  Phyllostictina  murrayae.  It  is  the 
belief  of  von  Hohnel  that  all  forms  similar  to  Phoma  uvicola  are  the 
conidial  stages  of  Guignardia  which  indeed  has  been  found  to  be  true 
of  Phyllosticta  paviae  Desm.  (Guignardia  aesculi  (Pk.)  Stewart)  and 
of  the  imperfect  form  of  Guignardia  vaccinii  Shear,  lately  named 
Phyllostictina  vaccinii  Shear.85  It  is  also  probable  that  Phyllosticta 
solitaria  E.  &  E.,  Phyllosticta  congesta  Heald  and  Wolf  and  other 
forms  like  Phoma  uvicola  are  related  to  Guignardia.  Shear,85  however, 
adhering  to  the  view  of  von  Hohnel,  has  regarded  Phyllosticta  solitaria 
E.&E.  as  a  good  Phyllostictina.  Roberts'70  study  of  Phyllosticta 
congesta  Heald  and  Wolf  shows  the  very  close  relation  of  this  fungus 
with  P.  solitaria  E.&E. 

In  Phoma  uvicola  and  Phyllosticta  solitaria  the  conidiophores  are 
always  present  (Fig.  6).  The  pycnidial  membrane  of  both  of  these 
forms  is  similar  altho  variable;  occasionally  thin,  and  at  times  thick- 
ened laterally  or  only  in  the  region-  of  the  ostiole.  The  pycnosclerotia 
are  often  somewhat  stromatic  and  always  have  thick,  dense  dothid- 


494 


BULLETIN  No.  256 


[February, 


eaceous  membranes.  Their  mode  of  spore  formation  differs  so  much 
from  our  present  conception  of  the  genus  Phyllosticta  that  these  forms 
might  rightfully  be  established  under  a  new  form  genus  in  the  main 
like  the  emended  description  of  Phyllostictina.  The  presence  of  a 
gelatinous  cap  or  appendage  on  the  spores  of  the  pycnosclerotia  of 
these  species  is  a  character  of  added  value  for  supporting  the  seg- 
regation. 

The  question  therefore 
arises  whether  to  create  a  new 
genus  for  Phoma  uvicola  B.  & 
C.  (not  Phyllostictina  uvicola 
(B.  &  C.)  v.  Hohnel)  and 
Phyllosticta  solitaria  E.  &  E., 
embodying  the  essential  char- 
acters of  the  emended  descrip- 
tion of  Phyllostictina  as  given 
by  von  Hohnel,  or  to  retain 
these  forms  in  the  form  genera 
Phoma  and  Phyllosticta  until 
critical  examination  of  the 
species  in  these  and  other  re- 
lated genera  is  possible.  The 
latter  course  appears  to  be  ad- 
visable ;  therefore,  for  the 


FIG.  8. — SECTION  THRU  A  PYCNOSCLEROTIUM 

FROM  CULTURE 
Note   gelatinous   threads   connecting   spores 


present,  the  original  name 
Phyllosticta  solitaria  E.  &  E. 
has  been  retained. 


PHYSIOLOGY 
Cultural  Characters 

Phyllosticta  solitaria  grows  readily  upon  almost  any  type  of  arti- 
ficial media,  but  it  grows  well  upon  a  medium  rich  in  carbohydrates. 
In  the  study  of  the  cultural  characters  of  the  fungus,  the  following 
types  of  media  were  employed:  apple-bark  corn-meal  agar,  Czapek's 
agar,  apple  agar,  apple  corn-meal  agar,  corn-meal  agar,  prune  agar, 
sterile  apple  twigs,  apple-bark  agar,  oat  agar. 

Apple  agar  was  prepared  by  heating  150  grams  of  chopped  apples 
in  distilled  water  in  a  boiling  water  bath  for  thirty  minutes,  then 
filtering  and  adding  to  the  filtrate  20  grams  of  granulated  sugar.  The 
volume  was  made  up  to  1,000  cc.  and  20  grams  of  agar  added.  Apple- 
bark  agar  was  prepared  similarly;  the  cortex  of  water  sprouts  and 
petioles,  and  leaves  being  employed  in  the  preparation  of  the  mixture. 
Combinations  of  these  media  were  prepared  by  mixing  together  equal 
parts  of  separate  media.  The  other  types  of  media  were  prepared 
according  to  standard  formulae. 


19  IS  5] 


APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL 


495 


Growth  is  manifested  as  a  spreading,  flat,  white,  round  colony, 
growing  superficially  upon  the  medium  and  only  slightly  penetrating 
it  (Fig.  7).  The  colony  may  advance  evenly  in  all  directions,  or  in  a 
wavy-bordered  fashion.  An  olivaceous  coloration  appears  very  early 
in  the  center  of  the  colony,  and  increases  in  area  with  the  increase 
in  area  of  the  colony.  On  oat  agar,  and  frequently  on  corn-meal  agar, 
the  olivaceous  coloration  fails  to  appear.  Growth  is  commonly 
olivaceous  and  with  age  becomes  black-olivaceous  and  almost  com 


FIG.  7. — APPLE  BLOTCH  FUNGUS  IN  CULTURE 
Note  the  flat,  spreading  character  of  the  growth 

and  the  numerous  black  pycnosclerotia.    Growing  on 

apple  agar  at  25°   C.  in  Petri  dish. 

pletely  black  in  the  interior.  With  the  appearance  of  the  dark 
olivaceous  coloration  in  the  center  and  the  light  olivaceous  coloration 
about  the  center,  the  colony  becomes  over-grown  by  a  short,  floccose, 
erect,  and  olivaceous  aerial  growth,  arising  first  in  the  center  of  the 
colony  and  advancing  outward. 

The  production  of  pycnosclerotia  (Fig.  8)  occurs  upon  almost  all 
types  of  artificial  media.  Apple  agars,  sterile  apple  twigs,  prune  agar, 
and  Czapek's  agar,  are  very  favorable  for  their  production.  Carbon- 
aceous, coal-black  pycnosclerotia  form  over  the  entire  inner  surface 
of  the  colony  giving  the  surface  a  crusty,  coal-black  appearance 
(Plate  3). 

On  Czapek's  agar,  prune  agar,  and  commonly  on  apple  agar,  the 
fungous  growth  eventually  becomes '  a  high,  irregular,  carbonaceous 


496  BULLETIN   No.   256  [February, 

mass  of  mycelium  and  pycnosclerotia.  This  type  of  growth  appears 
commonly  on  agar  slants  on  the  above  types  of  media,  but  rarely  in 
plates  on  these  media  excepting  on  Czapek's  medium  on  which  the 
colony  always  grows  in  a  high,  irregular  fashion.  On  corn-meal  or 
oat  agar,  on  the  other  hand,  growth  is  always  flat  and  spreading. 

Factors  Involved  in  Growth  and  Pycnosclerotia  Formation 

In  the  experiment  dealing  with  the  relation  of  temperature  and 
light  on  growth  and  pycnosclerotia  formation  various  types  of  media, 
previously  mentioned,  were  employed.  The  organism  was  transferred 
to  agar  plates  and  tubes,  and  placed  in  the  open  in  constant  tempera- 
ture chambers  of  5°,  10°,  15°,  20°,  25°,  and  30°  C.  An  equal  number 
of  plates  and  tubes  of  each  medium  were  placed  in  black,  cardboard, 
light-proof  boxes,  consisting  of  box  and  lid  which  permitted  of  easy 


t, 

FIG.  8. — SECTION  THRU  PYCNOSCLEROTIA  FKOM  CULTURE 
Note  character  of  the  pseudo-parenchymatous  interior 
and  thick  outer  coat. 

aeration.  These  temperature  chambers  were  located  in  greenhouses 
and  protected  against  direct  sunlight.  Constant  temperatures  were 
maintained  by  the  circulation  of  brine,  cooled  by  the  expansion  of  sul- 
fur dioxid.  The  brine  was  circulated  thru  the  chambers  by  an  elec- 
trically driven  pump,  and  the  temperatures  were  kept  constant  and 
uniform  in  the  chambers  by  thermostats  and  electrically  driven  fans. 
The  humidity  factor  was  not  under  control,  but  since  the  differences 
in  growth  and  production  of  pycnosclerotia  were  apparent  long  before 
any  drying  of  the  media  occurred,  the  effect  of  different  temperatures 
on  growth  and  pycnosclerotia  formation  may  be  regarded  as  relatively 
accurate. 

The  results  obtained  from  this  study  bear  evidence  that  growth 
and  pycnosclerotia  formation  of  Phyllosticta  solitaria  are  not  affected 


• 


PLATE  3. — CULTURES  OF  P.  solitaria,  SHOWING  TYPE  AND  MANNER  OF  GROWTH  ON 
DIFFERENT  SOLID  MEDIA  AND  THE  BLACK,  CARBONACEOUS  PYCNOSCL.EROTIA 

Tube  17,  on  Czapek  and  prune  agar  mixed;  20,  on  Czapek  and  apple-bark 
agar  mixed ;  21,  22,  on  apple  agar ;  23,  24,  on  apple-fruit  and  apple-bark  agar 
mixed;  25,  26,  on  Czapek  and  apple-fruit  agar  mixed. 


1925} 


APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL 


497 


TABLE  1. — INFLUENCE  OF  DIFFERENT  TEMPERATURES  UPON  THE  RATE  OF  APPEAR- 
ANCE OF  GROWTH  IN  OPEN  AND  IN  LIGHT-PROOF  BOXES 


Temperature 

5°C. 

10°C. 

15°C. 

20°C. 

25°C. 

30°C. 

35°C. 

Open  boxes    

Number  of  days  after  planting 

No  growth 
No  growth 

25-30 
30-35 

10-15 
10-12 

4 
4 

3 

2-3 

3 
2-3 

No  growth 
No  growth 

Light-proof  boxes  

TABLE  2. — INFLUENCE  OF  DIFFERENT  TEMPERATURES  UPON  THE  BATE  OF 
PYCNOSCLEROTIA  PRODUCTION  IN  OPEN  AND  IN  LIGHT-PROOF  BOXES 


Temperature  

5°C. 

10°G. 

15°C. 

20°C. 

25°C. 

30°C. 

35°C. 

Open  boxes  

Number  of  days  after  planting 

No  growth    1  30-35 
No  growth    |  30-40 

23 

18-25 

13 
11-13 

5-10 
5-8 

5-7 

5-8 

No  growth 
No  growth 

Light-proof  boxes  

by  light.  The  colonies  on  agar  plates  and  tube  slants  in  the  open, 
and  in  the  light-proof  boxes,  from  all  appearances  developed  and 
produced  pycnosclerotia  at  the  same  time.  There  was  no  evidence 
to  show  that  constant  darkness  had  a  repressive  effect  upon  growth  or 
pycnosclerotia  formation.  According  to  Coons18  light  is  a  decisive 
factor  in  the  reproduction  of  Plenodomus  fuscomaculans  regardless  of 
the  richness  or  poverty  of  the  substrata  in  nutrients.  With  that 
organism  there  is  also  a  strong  tendency  for  increased  growth  in  the 
dark.  The  results  of  Coons  and  Levine19  and  Levine50  indicate  that 
among  the  genera  of  Sphaeropsidales  many  species  are  definitely  light 
positive  to  pycnidia  formation  while  many  are  indifferent,  producing 
pycnidia  under  all  conditions.  Their  results  also  show  that  the  species 
of  one  form-genus  do  not  necessarily  behave  alike.  Phyllosticta  soli- 
taria  may  be  classed  among  those  species  which  are  indifferent  to  light. 

The  constant  presence  of  pycnidia  on  the  upper  sides  of  the  leaf 
blades  is  not  due  to  any  light  reaction,  but,  as  histological  studies 
show,  to  the  construction  of  the  leaf  and  the  supply  of  food.  The 
organism  grows  and  fruits  as  well  in  the  cavities  of  the  apple,  on  the 
pedicels,  and  on  the  bud  scales,  as  elsewhere  on  the  host.  These  tis- 
sues are  shaded  much  more  than  are  other  parts  of  the  host,  yet 
fruiting  does  not  seem  to  be  affected. 

The  relation  of  temperature  to  growth  and  pycnosclerotia  forma- 
tion is  significant  (Tables  1  and  2).  At  5°  C.  growth  is  completely 
suppressed.  At  10°  C.  growth  is  very  slow  and  does  not  become 
perceptible  on  the  surface  of  agar  until  twenty-five  to  thirty-five  days 
after  planting;  the  first  pycnosclerotia  are  apparent  from  thirty  to 
forty  days  after  planting.  At  15°  C.  the  organism  grows  slowly  altho 
better  than  at  10°  C. ;  the  earliest  apparent  growth  is  between  ten 
and  fifteen  days  after  planting.  At  20°  C.,  growth  is  manifested  in 


498  BULLETIN  No.  256  [February, 

four  days  and  the  pycnosclerotia  are  apparent  in  eleven  to  thirteen 
days. 

The  optimum  temperature  for  growth  and  pycnosclerotia  forma- 
tion lies  between  25°  and  30°  €.,  25°  C.  being  slightly  more  favorable 
than  30°  C.  At  both  temperatures  growth  is  evident  in  two  to  three 
days  and  pycnosclerotia  formation  in  five  to  eight  days  after  planting. 
At  35°  C.  the  fungus  does  not  grow,  showing  that  the  maximum  tem- 
perature for  growth  lies  between  30°  C.  and  35°  C.  (Table  1). 

Results  show  that  pycnosclerotia  production  occurs  at  all  tempera- 
tures favorable  to  growth,  and  that  where  growth  is  slow  the  forma- 
tion of  pycnosclerotia  is  slow.  At  the  extreme  temperatures  pycno- 
sclerotia production  is  less  in  proportion  to  growth  than  at  the  more 
favorable  temperatures,  which  indicates  that  growth  of  P.  solitaria 
occurs  at  slightly  wider  limits  than  the  production  of  pycnosclerotia. 

Thruout  this  study  it  was  evident  that  corn-meal  and  oat  agars, 
i.e.,  media  rich  in  protein,  were  not  favorable  for  pycnosclerotia  pro- 
duction, whereas  all  of  the  other  media  employed  induced  them 
abundantly. 

Spore  Production  in  Culture 

In  spite  of  the  rich  masses  of  pycnosclerotia  formed  on  artificial 
media  spores  were  rarely  produced.  In  regard  to  spore  formation  of 
P.  solitaria  Clinton17  states:  "Cultures  made  by  taking  diseased  tis- 
sues from  the  interior  of  affected  apples  produced  a  characteristic 
dark  olive-green  mycelium  that  formed  patches  of  rather  slow  growth 
on  the  medium  and  had  not,  after  two  months  development,  given  any 
sign  of  the  formation  of  a  spore  stage."  Scott  and  Rorer79  remark. 
"The  fungus  does  not  fruit  freely  on  culture  media,  and  so  far,  the 
writers  have  been  able  to  secure  spore-bearing  pycnidia  only  on  steril- 
ized apple  wood  and  corn  meal  agar.  Pycnidia-like  bodies  are  formed 
in  great  abundance  on  all  media,  but  these  are,  for  the  most  part, 
sterile.  In  apple-wood  cultures,  the  fungus  generally  fruits  well,  pro- 
ducing little  groups  of  pycnidia  rich  in  spores."  Lewis51  says,  "No 
spores  were  produced  on  prune  or  potato  agar  or  on  potato  cylinders, 
but  apple  wood  cultures  produced  spores  abundantly."  Roberts67 
states  in  a  discussion  of  cultural  relations  of  the  blotch  fungus, 
"Phyllosticta  solitaria  will  produce  pycnidia  on  all  of  the  ordinary 
solid  culture  media.  These  pycnidia,  however,  do  not  produce 
spores. ' '  He  was  able  to  grow  the  fungus  with  the  formation  of  both 
pycnidia  and  spores  only  on  sterile  apple  wood,  and  even  on  this 
medium,  two  to  three  months  elapsed  before  mature  spores  were  pro- 
duced. Stewart89  working  with  Guignardia  aesculi  found  that  cul- 
tures from  ascospores  and  from  diseased  horse  chestnut  leaves  de- 
veloped small  sclerotia-like  bodies  and  "altho  the  fungus  from  these 
two  sources  was  cultured  for  a  period  of  twelve  months  on  various 
media  no  fruiting  bodies  ever  developed." 


1-925]  APPLE  BLOTCH:    ITS  ETIOLOGV  AND  CONTROL  499 

The  writer  cultured  the  organism  repeatedly  on  different  media 
and  under  various  conditions.  Pycnosclerotia  production  always 
occurred,  but  spore  production  could  never  be  expected,  or  predicted 
with  any  measure  of  certainty.  The  pycnosclerotia  were  examined  for 
spores  at  short  intervals  for  a  period  of  two  months.  Spores  were  very 
rarely  found.  In  1919  the  writer  secured  spores  on  a  corn-meal  agar 
slant  at  25°  C.  in  seven  days  from  the  date  of  planting.  A  few 
pycnosclerotia  formed  on  the  colony,  but  on  sectioning  them,  it  was 
found  that  only  a  few  contained  spores  and  that  the  remainder  were 
sterile.  During  this  study  spore  production  occurred  a  few  times — on 
one  occasion  at  30°  C.  in  plates  on  a  mixture  of  Czapek's  and  apple 
media  and  again  at  25°  C.  on  oat  agar.  It  occurred  about  twenty-six 
days  after  planting  and  the  medium  then  was  completely  dry  and 
hardened. 

In  February,  1921,  the  fungus  was  isolated  from  cankers  on  vari- 
ously aged  bark  and  transferred  to  tubes  of  a  mixture  of  Czapek's 
and  apple  agar,  and  to  corn-meal  agar  containing  prune  juice.  Spore 
production  occurred  abundantly  in  several  of  these  cultures.  The 
age  of  the  canker  and  season  of  the  year  in  which  the  isolations  were 
made  seemed,  at  that  time,  to  have  some  influence  upon  spore  bearing. 
In  the  earlier  cultural  studies  most  of  the  isolations  from  the  host 
lesions  were  made  in  autumn  and  winter  while  the  organism  was  in 
an  inactive  condition,  but  no  spore-bearing  cultures  were  obtained. 
Further  attempts  early  in  the  season  in  later  years  and  in  the  spring 
of  1923,  with  mycelium  from  old  cankers  on  the  same  medium  and 
under  the  same  conditions  failed  to  obtain  fertile  pycnidia. 

Since  it  is  a  common  biologic  principle  that  suppression  in  growth 
generally  leads  to  reproduction,  the  writer  grew  the  organism  on  media 
in  "roll  cultures."  The  "roll  cultures"  were  prepared  by  rapidly 
rolling  tubes  containing  lOcc.  of  warm  mediurii  in  a  vertical  position 
between  the  palms  of  the  hands  with  the  base  of  the  tube  in  cold  water. 
In  such  tubes  the  medium  is  shallow,  and  consequently  the  mycelium, 
by  coming  in  direct  contact  with  the  glass  wall  of  the  culture  tube, 
would  eventually  become  starved,  a  condition  which  would  suppress 
growth  and  affect  fruiting.  The  "roll  cultures,"  however,  did  not 
induce  spore  production,  but  the  production  of  pycnosclerotia  was  as 
common  as  usual. 

Repeated  attempts  were  made  to  obtain  sporulation  by  subjecting 
the  pycnosclerotia  to  alternating  high  and  low  temperatures  (freezing 
them  and  restoring  them  to  warm  temperature).  The  results,  how- 
ever, were  all  negative.  Spores  were  obtained  abundantly  only  once 
in  pure  culture,  and  then  under  the  fluctuating  conditions  of  a  labora- 
tory. The  factors  favorable  to  sporulation  in  culture  remain  unknown. 

There  is  no  evidence  of  spore-bearing  strains  in  culture.  The  spore- 
bearing  cultures  obtained  by  the  writer  have  never  given  rise  to  others, 


500 


BULLETIN   No.   256 


[February, 


altho  the  same  medium  was  used  and  the  organism  was  incubated  in 
the  same  laboratory. 

Spore  Germination 

Germination  (Fig.  9)  is  first  manifested  by  a  small,  round  pro- 
tuberance occurring  most  commonly  on  the  narrow  end  of  the  spore. 


FIG.  9. — COMPARATIVE  DEVELOPMENT  OF  TUBES  OF  GERMINATING 
SPORES  AT  THE  END  OF  FORTY-EIGHT  HOURS  AT 

CONSTANT  TEMPERATURES 

(A)  Mature  spores  at  10°  C.,  (Ai)  immature  spores  bearing 
conspicuous  gelatinous  cap,  (B)  at  15°  C.,  (C)  at  20°  C.,  (D)  at 
25°  C.,  (E)  at  30°  C. 

In  practically  85  percent  of  the  germinations  the  germ  tube  arises 
from  the  narrow  pole,  about  10  percent  arise  from  the  sides  of  the 
spore,  and  the  remaining  5  percent  or  less  arise  from  the  broad  pole. 


1925]  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  501 

The  broad  pole  of  the  spore  bears  the  gelatinous  appendage  which 
evidently  serves  to  attach  the  spore  to  the  substratum  it  is  capable 
of  infecting.  The  primary  germ  tube  issues  usually  from  the  oppo- 
site ,end.  In  the  course  of  time  a  second  germ  tube  arises  commonly 
from  the  broad  end  of  the  spore.  The  cap  or  appendage  is  eventually 
dissolved ;  it  is  inconspicuous  on  mature  spores. 

In  contrast  to  the  successful  germination  of  spores  from  culture, 
the  spores  from  natural  sources  have  never  been  induced  to  germinate 
regularly  or  in  any  large  quantity.  During  the  spring  and  summer 
of  1920  and  1921,  from  April  15  to  July  15,  repeated  attempts  were 
made  to  germinate  spores  secured  from  pycnidia  on  leaves,  fruit,  and 
bark.  The  pycnidia  were  crushed  in  sterile,  tap,  or  rainwater,  and 
drops  of  the  suspension  were  placed  on  slides  in  moist  Petri  dishes  and 
kept  at  room  temperature.  Similar  mounts  to  which  crushed  pieces 
of  apple  peelings,  leaves,  or  bark  were  added  were  made  during  the 
spring  and  summer  of  1920  and  1921,  in  the  hope  that  these  might  in 
some  way  facilitate  spore  germination.  The  percentages  of  germina- 
tion were  small,  irregular,  and  generally  insignificant.  Occasional 
mounts  showed  a  trace  of  germination  and  rarely  high  percentages  of 
germination,  but  since  the  conditions  under  which  the  high  percentages 
of  germination  occurred  were  the  same  in  all  respects  as  those  where 
none  occurred,  it  is  difficult  to  explain  the  failures.  Roberts67  tested 
the  germination  of  spores  of  P.  solitaria  from  bark  cankers  and  ob- 
tained germination  in  distilled  water  after  May  23,  1914.  On  May 
13,  1915,  he  found  that  10  percent,  and  after  May  24,  75  percent  had 
germinated. 

The  conditions  necessary  for  spore  germination  are  moisture, 
nutrition,  favorable  temperatures,  and  maturity  of  the  spores.  Sterile 
distilled  water  is  not  a  favorable  medium  for  vigorous  and  successful 
germination  since  the  germ  tubes  grow  slowly  to  about  three  to  four 
times  the  length  of  the  spore  and  then  collapse  from  want  of 
nutrient.  In  sterile  distilled  water  the  percentage  of  germination 
is  small;  in  sterile  tap  water  it  may  reach  100  percent.  In  a  weak 
solution  of  apple  or  prune  extract,  the  germ  tubes  appear  early  and 
grow  vigorously,  and  finally  give  rise  to  mycelium. 

The  spores  do  not  germinate  well  unless  they  are  fully  matured. 
This  is  shown  by  attempts  to  germinate  spores  from  natural  sources 
before  the  occurrence  of  natural  infection,  or  from  pycnidia  from  the 
outer  living  portions  of  the  cankers,  even  after  primary  infection  has 
taken  place.  Spores  formed  in  the  pycnosclerotia  on  the  overwintered 
cankers  require  about  three  to  four  months  to  mature,  that  is,  from 
the  time  differentiation  begins  to  time  of  spore-discharge.  Spores  from 
young  spore-bearing  cultures  fail  to  germinate  even  in  a  nutrient 
medium  at  the  optimum  temperatures.  The  best  germination  was  ob- 


502 


BULLETIN   No.   256 


[February, 


tained  from  spore-bearing  cultures  one  to  one  and  one-half  months  old. 
From  a  culture  sixteen  days  old  the  germination  was  less  than  1  per- 
cent under  the  most  favorable  conditions.  Spores  from  a  culture  forty- 
six  days  old  under  similar  conditions  gave  100  percent  germination. 
In  spore  germination  the  temperature  is  of  extreme  importance. 
Pycnidia  were  taken  from  fertile  cultures  and  crushed  in  sterile  dis- 
tilled water,  or  in  a  weak,  sterilized,  nutrient  solution,  such  as  prune 
or  apple  fruit  extract,  and  the  volume  of  the  liquid  was  then  increased 
five  to  ten  times  in  order  to  avoid  crowding  the  spores.  The  prune 
extract  was  prepared  by  cooking  two  or  three  prunes  in  200  cc.  of 
distilled  water;  the  apple  extract  was  made  similarly  from  fresh 
apples.  The  extracts  were  filtered  and  sterilized  before  using.  The 
spores  were  germinated  on  slides  in  Petri  dishes  at  constant  tempera- 

•i*.<;?.-.^.  :;_••)?  K;;  -  :    :       -jyl 
TABLE  3. — BATE  AND  PERCENTAGE  OF  GERMINATION,  AT  DIFFERENT  TEMPERATURES, 

OF  SPORES  FROM  CULTURE  32  DAYS  OLD 
Spores  suspended  in  a  weak  sterilized  solution  of  apple  extract 


Hours  after  sowing 

10                20 

32 

45        |       70 

95 

117 

Temperature 

Percentage  germination 

41°F.  :    5°C... 

0 
0 
t 
1 
2 
0 

0 
t 
1 
2-3 
5 
1 

0 
t 
1-5 
15-20 
25 
1 

0 
1 
5, 
20 
30 
1 

0 
1 

10-15 
50 
50 

(Practici 

t 
5-10 
20 
50 

50-60 
lly  no  gerr 

,;:-.t;  f 
10 
20-25 
50 
50-60 
r  nation) 

50°F.  :  10°C  

58°F.  :  15°C  

68°F.  :  20°C  

77°F.  :  25°C  

86°F.  :  30°C  

t  =  trace. 

-,.;:  -   •  .  .  -•;,) ,-;    ..•  :•<.•..    .".  •{  ;•:.;• .  :  .-  =...:• 

tures.  Drops  of  the  spore  suspension  were  placed  on  slides  and  two 
slides  were  placed  in  each  dish  on  glass  rods  with  moistened  filter 
paper  in  the  bottom  of  the  dish  with  sufficient  water  to  maintain 
moist  conditions. 

The  results  in  Table  3  are  based  on  spores  from  a  culture  thirty- 
two  days  old.  The  percentage  of  germination  is  not  high,  evidently 
owing  to  the  immaturity  of  the  spores.  After  an  exposure  of  167 
hours,  the  Petri  dishes  in  the  5°,  10°,  and  15°  C.  chambers  were  trans- 
ferred to  the  20°  C.  chamber  where,  within  132  hours,  40  to  60  per- 
cent of  the  spores  had  germinated  and  developed  hyphae. 

The  results  in  Table  4  were  obtained  with  spores  from  a  culture 
forty-six  days  old.  They  show  that  with  this  increased  age  of  the 
pycnidia  there  was  increased  percentage  of  germination.  At  15°,  20°, 
25°,  and  30°  C.,  100  percent  germination  was  eventually  present,  but 
the  rate  of  development  of  the  germ  tubes  was  most  extensive  and 
rapid  at  25°  and  30°  C.  After  an  exposure  of  101  hours  at  5°  and 
10°  C.  the  Petri  dishes  were  placed  in  the  25°  C.  chamber,  where  at  the 
end  of  thirteen  hours  about  80  percent  of  the  spores  had  germinated, 
and  at  the  end  of  twenty -five  hours  from  80  to  100  percent. 


1925} 


APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL 


503 


TABLE  4.— BATE  AND  PERCENTAGE  or  GERMINATION,  AT  DIFFERENT  TEMPERATURES, 

OF  SPORES  FROM  CULTURE  46  DAYS  OLD 
Spores  suspended  in  a  weak  sterilized  solution  of  apple  extract 


Hours 

after  sowing  

7 

17 

31 

42 

73 

Temperature 

Percentage  germination 

41°F. 

5°C... 

0 
0 
0 
0 
t 
30-40 

0 
0 
3 

40-50 
95 
90-100 

0 

t 
30-40 
90-95 
95-100 
9.5-100 

0 

t 
80 
95-100 
(Excellent  g 
(Excellent  a, 

0 

t 
90-100 
100 
ermination) 
ermination) 

50°F. 
59°F. 
68°F. 
77°F. 
86°F. 

10°C  
15°C  

20°C  
25°C  

30°C  

t  =  trace. 

The  results  in  Table  5  are  based  on  spores  from  a  culture  thirty- 
four  days  old.  The  spores  were  suspended  in  sterile  distilled  water. 
The  germination  was  low  at  first,  altho  it  increased  later  even  at  the 
lower  temperatures.  The  growth  of  the  germ  tubes  was  checked  early. 
After  132  hours  the  Petri  dishes  in  the  5°  C.  chamber  were  trans- 
ferred to  the  20°  C.  chamber  and  good  germination  resulted,  altho  the 
germ  tubes  were  poorly  developed. 


TABLE  5. — BATE  AND  PERCENTAGE  OF  GERMINATION,  AT  DIFFERENT  TEMPERATURES, 

OF  SPORES  FROM  CULTURE  34  DAYS  OLD 

Spores  suspended  in  sterile  distilled  water 


Hours  after  sowing    

12 

21 

35 

59 

108 

Temperature 

Percentage  germination 

41°F.       5°C  

.0 
0 
t 
t 
1 
2-4 

0 
0 
t 

1 

10 
50 

0 
t 
1-2 

10 
15 
50 

0 
t 
20-30 
30 
30-40 
50 

0 
t 

25-30 
30-40 
40-50 
60 

50°F.     10°C  

59°F.     15°C  

68°F.     20°C  
77°F.    25°C  

86°F.     30°C  

t  =  trace. 

In  Table  6  the  mounts  were  made  from  a  culture  forty-eight  days 
old.  Petri  dishes  exposed  to  5°,  10°,  and  15°  C.  respectively  for 
seventy-one  hours  were  transferred  to  25°  C.  and  at  the  end  of  four- 
teen hours  some  germination  had  occurred  at  5°  C.,  and  50  to  60  per- 
cent at  10°  and  15°  C. 

In  Table  7  the  germinations  were  conducted  in  a  laboratory  where 
the  temperatures  fluctuated  between  13°  and  24°  C.  The  spores  were 
from  a  culture  thirty-four  days  old. 

The  data  in  the  above  tables  show  that  the  optimum  temperature 
for  spore  germination  lies  around  30°  C.  (86°  F.),  and  that  the  rate 
of  growth  of  the  germ  tubes  is  greatest  at  25°  C.  (77°  F.)  and 
30°  C.  (86°  F.).  At  the  lower  temperatures,  namely  15°  C.  (59°  F.) 


504 


BULLETIN   No.   256 


[February, 


TABLE  6. — RATE  AND  PERCENTAGE  or  GERMINATION,  AT  DIFFERENT  TEMPERATURES, 

OF  SPORES  FROM  CULTURE  48  DAYS  OLD 
Spores  suspended  in  sterile  distilled  water 


Hours  after  sowing  

11 

17 

34 

46 

71 

Temperature 

Percentage  germination 

41°F.      5°C... 

0 
0 
0 
0 
0 
5-10 

0 
0 
0 
0 
30 
40-50 

0 
0 
t 
30-40 
50-60 
60-70 

0 
0 

t 
40 
60-70 
60-70 

0 
0 
t 
40-50 
60-70 
70 

50°F.     10°C  

59°F.     15°C  

68°F.     20°C  

77°F.     25°C  

86°F.     30°C  

TABLE  7. — RATE  AND  PERCENTAGE  OF  GERMINATION,  UNDER  LABORATORY  TEMPERA- 
TURES, OF  SPORES  FROM  CULTURE  34  DAYS  OLD 


Hours  after  sowing  

12 

24 

36 

60 

Media  used 

Percentage  germination 

Sterile  water    

t 
t 
0 
t 

50 
60 
0 
90 

50 
70-90 
2-10 
100 

95 
100 
25-35 
100 

Weak  sugar  solution  

Apple-bark  extract  

Apple  fruit  juice  

t  =  trace. 

and  20°  C.  (68°  F.),  the  amount  of  germination  at  first  is  small  and 
the  growth  of  the  germ  tubes  is  slow,  altho  with  longer  exposures  100 
percent  germination  is  obtained  in  nutrient  solutions,  including  sterile 
tap  water  (Fig.  9,  B  and  C).  At  15°  C.  (59  F.)  branching  and 
anastomosing  of  the  germ  tubes  are  rare,  while  at  20°  C.  (68°F.), 
altho  growth  is  slow,  hyphae  ultimately  appear.  At  5°  C.  (41°  F.) 
and  10°  C.  (50°  F.)  germination  rarely  occurs  and  then  growth  never 
exceeds  twice  the  length  of  the  spore  (Fig.  9,  A). 

The  spores  remain  viable  in  moisture  for  some  time  under  tempera- 
tures low  enough  to  inhibit  germination.  Since  spores  from  pure  cul- 
ture were  rarely  obtained,  no  studies  could  be  undertaken  to  deter- 
mine the  longevity  of  the  spores  under  various  conditions;  however, 
the  above  results  show  that  when  spores  are  exposed  to  a  tempera- 
ture of  5°  C.  (41°  F.)  for  one  week  they  remain  viable  and  germinate 
normally  when  introduced  into  higher  temperatures.  Undoubtedly 
the  spores  can  survive  much  longer  periods  under  these  conditions. 
This  is  significant  since  under  natural  conditions  in  prolonged  periods 
of  rain  and  low  temperatures  spores  may  remain  viable  and  produce 
infection  when  favorable  temperatures  are  obtained. 


1925]  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  505 

LIFE  HISTORY 
Inoculation  and  Infection 

Scott  and  Rorer79  report  the  successful  infection  of  the  leaves  and 
fruit  of  the  apple  with  spores  obtained  from  bark  cankers  and  apple 
blotches.  Numerous  small  blotches  were  found  on  the  fruits,  leaf 
blades,  and  petioles  in  one  month,  but  no  bark  cankers  resulted.  One 
tree  which  was  atomized  with  sterile  water  as  a  check  showed  no  signs 
of  the  disease.  The  experiment  of  Scott  and  Rorer  is  far  from  con- 
clusive since  they  report  the  results  of  but  a  single  experiment  with- 
out the  use  of  pure  culture  and  in  a  territory  where  blotch  was  seri- 
ously prevalent. 

Roberts67  infected  successfully  the  foliage,  fruits,  and  twigs  of 
the  Missouri  Pippin  with  spores  of  Phyllosticta  solitaria  obtained  from 
pure  culture.  The  spores  were  suspended  in  sterile  water  and  sprayed 
upon  the  host  in  early  July.  The  disease  appeared  a  month  later. 
His  attempts  to  infect  the  fruit  of  the  Missouri  Pippin  and  Ben  Davis 
after  August  1  were  unsuccessful.  Roberts68  states,  "  Infection  can 
take  place  only  on  the  young  branches  of  the  current  year's  growth. 
Vigorously  growing  water  sprouts  are  especially  susceptible." 

The  writer  has  been  unsuccessful  in  securing  artificial  infection. 
In  the  winter  of  1921  spores  were  obtained  abundantly  on  artificial 
media  and  when  properly  matured,  as  indicated  by  the  high  per- 
centages of  germination,  they  were  suspended  in  water,  sprayed  with 
an  atomizer,  and  sprinkled  on  potted  one-year-old  Duchess  apple 
trees  in  inoculating  chambers.  The  trees  were  grown  in  the  green- 
house for  a  month  or  more  and  the  foliage  was  abundant.  Clusters 
of  leaves  were  also  atomized  and  enclosed  in  transparent  parchment 
paper  bags.  In  each  sack  moist,  absorbent  cotton  was  placed  in  order 
to  insure  moist  conditions.  All  such  attempts  were  unsuccessful.  The 
failure  to  obtain  spores  in  quantity  in  pure  culture  eliminated  all 
hope  of  conducting  artificial  inoculations  with  spores  under  aseptic 
conditions. 

During  two  seasons'  work  in  southern  Illinois,  many  attempts 
were  made  to  produce  the  disease  artificially  with  spores  obtained  from 
host  lesions.  One-year-old  Duchess  trees  were  secured  from  a  northern 
nursery  and  planted  in  pots.  Pycnidia  were  crushed  in  sterile  water, 
tap  water,  or  rain  water,  and  the  spore  suspension  was  applied  to  the 
new  growth  with  an  atomizer.  Transparent  parchment  paper  bags 
containing  moist  cotton  were  then  placed  over  the  atomized  foliage 
and  the  bags  were  moistened  frequently.  Despite  the  many  attempts 
no  infections  resulted. 

Similar  efforts  were  made  to  infect  the  healthy  fruit  and  foliage 
of  bearing  Duchess  and  Benoni  trees  with  spores  obtained  from 
natural  sources.  Before  natural  infection  occurred  transparent  parch- 


506  BULLETIN  No.  256  [February, 

ment  paper  bags  were  placed  over  and  tied  around  the  new  growth  of 
foliage  and  fruit  as  a  protection  against  natural  infection.  Fre- 
quently, thruout  the  season,  some  of  the  bags  were  removed  and  the 
healthy  growth  atomized  with  a  water  suspension  of  spores,  this  being 
done  when  possible  before  rains  and  in  the  evening.  After  atomiza- 
tion  a  handful  of  wet  absorbent  cotton  was  placed  around  the  stem 
and  the  growth  was  covered  by  a  fresh  bag,  and  moistened.  For 
every  group  of  protected  growths  atomized  with  spores,  two  or  three 
bagged  growths  were  atomized  with  sterile  water  to  serve  as  checks. 
Similar  trials  were  made  using  glass  flasks  and  chimneys  containing 
moist  cotton  in  place  of  the  parchment  paper  bags.  Infections  were 
never  obtained. 

The  difficulty  of  securing  spores  in  pure  culture  and  artificially 
infecting  the  host  likewise  has  been  encountered  with  Guignardia 
bidwellii,  G.  aesculi,  and  G.  vaccinii.  Reddick66  was  unable  to  obtain 
successful  infections  of  the  grape  with  pycnospores  of  Guignardia 
bidwellii;  he  states,  ' '  The  writer  is  utterly  at  a  loss  to  understand  his 
failures  to  obtain  infections. ' '  Shear84  was  unable  to  infect  the  cran- 
berry artificially  to  thereby  discover  exactly  when  and  in  what  manner 
infection  of  the  leaves  and  fruit  takes  place.  He  found  that  the 
majority  of  cultures  of  Guignardia  vaccinii  were  either  entirely  sterile 
or  produced  only  pycnosclerotia. 

Sources  of  Inoculum 

The  fruiting  bodies  in  the  central  areas  of  the  cankers  are  matured 
and  free  of  spores  earlier  in  the  season  than  those  in  the  outer  areas. 
Primary  infections,  therefore,  are  evidently  the  result  of  spores  from 
pycnosclerotia  confined  to  the  older  areas  of  the  canker,  the  pycnidia 
on  the  outer  areas  serving  as  sources  of  inoculum  for  later  infections. 
Owing  to  the  slow  advance  of  the  cankers  during  the  late  spring  and 
summer,  inoculum  from  the  cankers  during  the  season  is  practically 
limited  to  the  fruiting  bodies  formed  prior  to  the  fall  of  the  bloom. 
The  irregular  and  continued  discharge  of  spores  from  the  pycnidia 
on  the  cankers  is  responsible  for  repeated  infections  thruout  the  spring 
and  summer.  After  August,  infections  from  these  sources  cease,  for 
the  supply  of  spores  becomes  exhausted  and  only  pycnosclerotia  are 
formed.  The  new  cankers,  which  appear  in  August,  likewise  bear  only 
pycnosclerotia  which  function  the  following  spring. 

After  leaf  petioles,  blades,  pedicels,  and  fruit  are  infected,  the 
sources  of  inoculum  later  in  the  season  are  naturally  increased  many 
times.  The  pycnospores  from  the  lesions  on  the  leaves  infect  the  same 
leaves  and,  as  new  lesions  appear  on  the  fruit  and  leaves,  new  sources 
of  inoculum  arise.  Infections  resulting  from  inoculum  from  these 


1985]  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  507 

sources  cease  in  August,  since  the  supply  of  spores  becomes  exhausted, 
and  the  organism  produces  only  pycnosclerotia. 

The  pycnosclerotia  also  overwinter  on  the  mummies  and  fallen 
leaves.  In  the  spring  these  pycnosclerotia  either  remain  sterile  or 
produce  pycnospores,  but  in  the  absence  of  evidence,  the  significance 
of  these  spores  is  uncertain.  In  view  of  the  location  of  mummied 
fruit  and  decaying  leaves,  and  the  adhesive  quality  of  the  spores  when 
exuded  under  moist  conditions  it  would  seem  that  the  influence  of 
gravity  and  washings  from  rain  would  carry  the  spores  away  from 
the  action  of  wind  and  a  favorable  substratum. 

The  relation  of  the  location  of  diseased  fruit  and  foliage  to  the 
location  of  the  cankers  supports  the  view  that  the  inocula  causing 
primary  infections  arise  from  the  bark  cankers.  This  relationship  is 
best  observed  on  lightly  infected  trees.  With  the  first  appearance  of 
the  disease  on  the  leaves  and  fruit,  close  observations  show  that  the 
first  symptoms  of  the  disease  are  always  close  to,  and  associated  with, 
the  bark  cankers.  A  very  clear  ease  of  such  a  relationship  was  found 
at  Mount  Morris  (111.)  in  1920.  On  only  one  tree  in  a  Northwestern 
Greening  orchard,  did  the  writer  find  a  cluster  of  blotched  apples  on 
a  spur,  accompanied  by  infected  leaves.  A  lone  canker  was  on  a 
branch  directly  above.  In  no  instance  has  it  been  possible  to  trace 
primary  infections  to  any  source  but  the  cankers,  a  fact  which  is 
universally  recognized  in  the  literature  on  this  disease. 

Time  of  Infection 

The  periods  of  infection  have  been  studied  for  three  years  at  vari- 
ous localities  in  Illinois.  The  plan  involved  the  daily  presence  of  the 
writer  in  the  orchard  under  observation,  bagging  of  fruit  and  foliage, 
compilation  of  daily  weather  data,  spraying,  and  other  orchard  opera- 
tions. The  results  obtained  with  bags  correlated  with  weather  data 
have  made  it  possible  to  arrive  at  valuable  information  regarding  the 
dates  of  primary  infection  and  the  frequency  of  infections  during 
the  season. 

The  bags  were  of  white,  stiff,  transparent,  parchment  paper  bear- 
ing a  disk  at  the  upper  end  to  whichj  a  string  was  attached  for  tying. 
Two  sizes  were  employed,  H/o  by  5V4  inches  for  the  fruit,  and  141/2 
by  8  inches  for  water  sprouts  and  terminal  twig  growth.  When  the 
bags  were  first  used  it  was  found  that  often  in  rainy  weather  the 
glued  edges  came  apart.  An  application  of  hot  paraffin  to  the  edges 
of  the  bags  before  use  insured  their  security  during  rainy  weather. 

The  bagging  operations  were  conducted  as  follows:  A  few  days 
after  petal  fall,  in  dry,  fair  weather,  several  bags  were  tied  over  the 
fruit  and  twigs  of  severely  cankered  trees.  At  regular  intervals 
thereafter,  until  the  first  symptoms  of  the  disease  on  the  fruit  and 
foliage  became  apparent,  additional  bags  were  placed  on  other  fruits 


508 


BULLETIN   No.   256 


[February, 


and  twigs.  Likewise,  at  regular  intervals,  bags  were  removed  during 
the  course  of  the  season  tho  many  bags  were  left  on  until  September 
to  serve  as  cheeks.  But  one  apple  and  a  few  leaves  were  limited  to 


FIG.  10. — BAGS  USED  TO  DETERMINE  TIME  AND  DURATION  OP 

NATURAL  INFECTION 

Above,  on  Duchess  trees;    below,  on  Sops  of  Wine  trees. 
Anna,  May,  1921. 

a  single  small  bag.  When  more  than  one  apple  was  present  on  the 
spur  the  others  were  removed,  thus  allowing  for  the  better  develop- 
ment of  the  apple  and  avoiding  the  danger  of  breaking  the  bag.  The 
larger  bags  allowed  covering  of  entire  fruit  clusters.  To  facilitate 


1925] 


APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL 


509 


placing  and  tying  the  bag  about  the  fruit  and  twigs,  the  leaves  on 
a  few  of  the  nodes  of  the  preceding  season's  growth  were  removed. 
Because  of  the  stiffness  of  the  parchment  paper  when  dry,  tearing 
cannot  be  avoided  in  opening  and  tying  unless  the  bag  is  first  moist- 
ened. A  short  wetting  before  opening  and  tying  permits  of  firm 
tying  about  the  twig  and  thus  avoids  any  danger  of  infection  enter- 


FIG.  11. — COMPARATIVE  SIZE  OF  FOUR  SUSCEPTIBLE  VARIETIES  OF 
APPLES  AT  THE  TIME  OF  FIRST  HEAVY  INFECTIONS 

AT  ANNA,  1921 

Upper  left,  Duchess;    upper  right,  Sops  of  Wine;    lower  left, 
Ben  Davis;   lower  right,  Benoni. 

ing  the  bag  at  this  point.  The  bag  is  placed  over  the  growth  and 
the  upper  portion  is  gathered  together  and  wrapped  evenly  about  the 
twig,  and  the  string  is  wrapped  a  few  times  below  the  disk,  then  at 
the  base  of  the  new  growth  and  a  few  times  about  the  disk.  The 
tyings  must  not  be  too  tight  and  care  must  be  taken  to  exclude  any 
portion  of  the  previous  season's  growth,  since  the  presence  of  cankers 
in  the  bag  would  destroy  the  value  of  the  experiment.  On  drying, 
the  bags  become  stiff  and  if  the  tying  is  done  properly,  growth  pro- 
ceeds as  with  the  unbagged  fruit  (Fig.  10).  The  protected  fruit 


510 


BULLETIN   No.   256 


[February, 


matures  somewhat  earlier  than  the  unbagged  fruit,  but  this  does  not 
vitiate  the  accuracy  of  the  data  since  infection  is  possible  even  when 
the  fruit  and  foliage  are  nearly  mature. 

Season  of  1920  at  Anna. — The  bagging  was  conducted  on  the 
Duchess  variety  (Table  8).  The  first  bags  were  put  on  May  1  and  2. 
Petal  fall  (75  percent  fallen)  occurred  on  April  25  and  26  and  the 
calyx  spray  was  applied  on  April  26  and  27.  The  first  infections  of 
the  season  occurred  during  the  rains  of  May  11,  12,  and  13,  or  fifteen 
to  eighteen  days  after  the  recorded  period  of  petal  fall.  Further 
infections  occurred  during  the  rains  of  May  16,  17,  and  18,  May  30 


FIG.  12. — THERMOGRAPH  AND  PRECIPITATION  RECORDS  IN  ANDERSON  ORCHARD, 

ANNA,  MAY  9  TO  17,  AND  MAY  29  TO  JUNE  4,  1920 
Time  periods  for  Duchess  variety;    precipitation  for  twenty-four  hour 
period,  evening  to  evening. 

and  31,  and  June  3.  The  first  spray  for  blotch  was  applied  on  May  14 
and  15,  and  spraying  was  continued  at  weekly  intervals  during  May 
and  June.  The  failure  to  apply  the  first  blotch  spray  ahead  of  the 
rainy  period  of  May  11  to  13  resulted  in  poor  control  in  every  plat. 
In  bags  that  were  put  on  May  12  and  13,  and  removed  on  June  11, 
there  was  present,  with  one  exception,  an  abundance  of  fruit  and 
petiole  infection.  This  shows  that  primary  infections  occurred  be- 
tween May  2  and  May  14,  and  from  a  study  of  the  local  weather 
records  (Fig.  12)  the  primary  infection  of  Duchess  fruit  and  foliage 
must  have  occurred  on  May  11,  12,  and  13.  The  disease  was  found 
on  May  27  for  the  first  time  in  the  season. 

The  data  show  (Table  8)  that  the  disease  was  not  present  on  foliage 
protected  up  to  June  4,  when  examined  on  July  15.  However,  growth 
protected  up  to  June  4  and  examined  on  September  11,  revealed  seri- 
ous infection  of  the  petioles.  Study  of  the  weather  after  June  4 
shows  that  small  precipitations  occurred  on  June  19,  21,  22,  July  2, 
5,  and  that  heavy  rain  occurred  on  July  13  and  July  18.  Since  two  to 

70 


19S5] 


APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL 


511 


TABLE  8. — EESULTS  OF  BAGGING  EXPERIMENTS  ON  DUCHESS  TREES,  ANDERSON 

ORCHARD,  ANNA,  1920 


No.  of 
bags 

Date  put 
on 

Date  taken 
off 

Infection 

Second  examination 

Date 

Infection 

5 

May  1  and  2 

June    4 

_ 

July   15 

_ 

7 

— 

Sept.  11 

S.p.i. 

1 

" 

— 

M.p.i. 

3 

June    6 

— 

July   15 

— 

7 

— 

Sept.  11 

S.p.i. 

1 

44 

— 

— 

5 

June    8 

— 

July   15 

— 

3 
3 

.! 

I 

Sept.  11 

Sp.i. 
M.p.i. 

1 

" 

— 

5 

June  11 

— 

July   15 

— 

2 

— 

Sept.  11 

— 

6 

" 

— 

S.p.i. 

5 

June  16 

— 

July   15 

— 

5 

" 

— 

Sept.  11 

S.p.i. 

5 

June  20 

— 

July   15 

— 

5 
0 

June  25 

— 

Sept.  11 
July   15 

S.p.i. 

2 

— 

Sept.  11 

— 

5 

44 

— 

S.p.i. 

2 

July     2 

— 

S.p.i. 

5 

— 

— 

5 

July     9 

_ 

S.p.i. 

3 

" 

—  ' 

— 

2 
1 

July   13 

I 

S.p.i. 
M.p.i. 

1 

" 



— 

20  (checks) 

Sept.  11 

Found  in  1  bag 

8 

July     2 

— 

July   15 

— 

4 

May  12 

June  11 

S.f.  &  p.i. 

1 

*' 

41 

— 

3 

May  13 

44 

S.f.  &  p.i. 

3 

May  14 

44 

S.f.  &  p.i. 

1 

44 

— 

3 

May  17 

44 

S.f.  &  p.i. 

1 

44 

S.  p.  i. 

6 

May  21 

14 

S.f.  &  p.i. 

1 



0 

May  23 

S.f  &p.i. 

(  -  )=:  disease  not 
ate  petiole  infection  ; 


present  ;    S.p.i.  =  severe  petiole  infection  ;    M.p.i.  =  moder- 
S.f. &  p.i.  =  severe  fruit  and  petiole  infection. 


three  weeks  are  required  for  the  symptoms  to  become  apparent  on 
fruit  and  foliage,  it  seems  that  the  small  precipitations  between  June 
4  and  July  15  were  insignificant  and  not  favorable  for  infection.  The 
precipitations  of  July  13  and  18  were  large  enough  for  infection,  and 
the  constancy  of  the  disease  on  the  foliage  when  examined  on  Sep- 
tember 11  indicates  that  infection  occurred  during  these  rains,  as 
well  as  during  the  heavy  rains  of  August  8  to  10  and  15.  The  re- 
maining days  of  these  two  months  were  marked  by  dry  weather  and 
occasional  short  rains  unfavorable  for  infection.  When  the  bags  were 
removed  at  intervals  during  the  period  June  4  to  July  13,  and  the  fruit 
and  foliage  examined  on  July  15,  the  disease  was  universally  absent, 
and  when  this  same  growth  was  examined  on  September  11,  the  dis- 
ease, with  a  few  exceptions,  was  universally  present.  Heavy  infections, 
therefore,  occurred  during  July  and  August. 

Season  of  1921  at  Anna.  —  The  bagging  experiments  in  this  season 
were  conducted  on  the  Duchess  variety  (Table  9).     The  season  was 


512 


BULLETIN   No.   256 


[February, 


TABLE  9. — RESULTS  OF  BAGGING  EXPERIMENTS  ON  DUCHESS  TREES,  MILLER 
ORCHARD,  ANNA,  1921 


No.  of 
bags 

Date  put 
on 

Date  taken 
off 

Infection 

Second  examination 

Third  examination 

Date 

Infection 

Date 

Infection 

2 
2 

April  18 

May  23 

- 

Sept.    7 
July   15 

S.p.i. 

3 

" 

May  25 

— 

" 

44 

2 

May  28 

— 

** 

44 

1 

" 

— 

M.p.i. 

Sept.    7 

S.p.i 

4 

" 

May  31 

— 

44 

S.p.i. 

1 

— 

Sept.    7 

4 

1 

June     4 

— 

July    15 

44 

1 

• 

" 

— 

M.p.i 

M.p.i. 

1 

* 

June  10 

— 

" 

S.p.i. 

Defoliated 

2 

• 

— 

Sept.    7 

3 

1 

! 

June  21 

— 

July   15 

— 

S.p.i 
M.p.i. 

1 

* 

June  28 

— 

*4 

— 

S.p.i 

3 

• 

— 

Sept.    7 

M.p  i. 

1 

July     8 

— 

S.p.i 

2 

* 

July    15 

— 

14 

M.p»i. 

1 

* 

— 

44 

S.p.i. 

1 

• 

July  28 

_ 

44 

M.p.i. 

1 

*' 

Trace 

44 

S.p.i. 

8  (checks) 

• 

Sept.    9 

— 

1  (check) 

April  21 

" 

— 

1 

April  22 

July   15 

— 

44 

M.p.i. 

1 

" 

'* 

— 

44 

S.p.i. 

2 

11 

July  28 

— 

44 

7 

April  25 

June  16 

— 

44 

1 

" 

July   15 

— 

44 

1 

*' 

Trace 

2 

" 

July  28 

— 

44 

M.p.i. 

1 

*' 

44 

Trace 

44 

Sp.i. 

1 

April  26 

July   15 

S.p.i. 

44 

1 

44 

— 

4 

1 

" 

July   28 

Trace 

4 

1 

" 

" 

— 

4 

3 

April  27 

June  16 

— 

4 

1 

" 

Trace 

4 

1 

May    2 

July  28 

— 

4 

1 

** 

S.p.i. 

4 

1 

" 

" 

Trace 

4 

1 

May    3 

S.p.i. 

2 

•* 

** 

Trace 

1 
1 

May    5 

June  16 

July    15 

Sept.    7 

S.p.i. 

1 

** 

" 

— 

Sept.    7 

1 

July   28 

Trace 

1 

May     7 

July     8 

— 

July   15 

— 

44 

Trace 

1 

H 

July   15 

— 

Sept.    7 

M.p.i. 

1 

11 

July   28 

— 

1 

** 

44 

Trace 

44 

S.p.i. 

2 

May  12 

June  16 

S.p.i. 

July   15 

1 

** 

4 

May  16 

" 

' 

4 

May  19 

*4 

* 

1 

May  31 

1 

July    15 

* 

1 

July   28 

2 

June     4 

Scot.    7 

(-)= 

ate  petiole 


:  disease  not  present ;    S.p.i.  =  severe  petiole  infection ;    M.p.i.  =:  moder- 
infection. 


abnormal.  The  trees  bloomed  very  early  and  three  successive  frosts 
destroyed  the  major  portion  of  the  crop.  In  the  absence  of  much 
fruit,  only  twig  growth  with  leaves  could  be  bagged;  but  since  both 
leaf  and  fruit  infection  occur  at  the  same  time  and  under  the  same 
conditions,  the  data  obtained  are  applicable  to  fruit  infection  as  well. 
Petal  fall  for  the  Duchess  orchard  was  recorded  for  April  6  and  7. 
The  first  bags  were  removed  and  new  ones  put  on  at  intervals  of  two 


1925]  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  513 

or  three  days.  The  first  bags  were  put  on  April  18,  and,  as  the 
data  show  (Table  9)  the  disease  was  not  present  when  these  bags  were 
removed  at  various  intervals  from  May  23  to  September  9,  indicating 
that  no  infection  occurred  prior  to  April  18.  Of  a  total  of  thirty-four 
bags  put  on  during  the  period  April  25  to  May  7,  twenty-one  growths 
were  disease-free,  thirteen  showed  disease,  three  of  which  showed 
severe  infection,  and  ten  traces  of  infection.  The  primary  infections, 
therefore,  could  not  have  been  heavy.  A  study  of  the  weather  records 
shows  that  ideal  conditions  for  infection  occurred  on  April  26  and  27, 
about  nineteen  days  after  petal  fall.  The  disease  was  apparent  on 
Duchess  fruit  and  foliage  on  May  19.  The  first  heavy  infections,  how- 
ever, occurred  during  the  period  May  9  to  12;  a  period  five  weeks 
after  petal  fall,  marked  by  continuous  damp,  foggy  weather,  and 
precipitations  amounting  to  1.58  inches.  As  the  season  was  abnormal 
no  significance  can  be  attached  to  the  relation  of  the  time  elapsing 
between  petal  fall  and  infection  (Fig.  11).  The  data  (Table  9)  fur- 
ther show  that  growth  covered  at  intervals  during  the  period  May  12 
to  June  4  was  severely  diseased  on  examination  later  in  the  season. 

Heavy  infections  occurred  again  in  June.  The  data  show  (Table  9) 
that  when  bags  were  applied  April  18,  and  removed  at  intervals  from 
May  23  to  June  10,  no  disease  was  present,  and  that  when  this  same 
growth  was  examined  on  July  15  disease  was  universally  present.  A 
study  of  the  weather  after  May  9  to  12  shows  that  infection  could 
only  have  happened  on  June  19  to  21  during  a  precipitation  of  3.7 
inches,  2.99  inches  of  which  fell  on  June  19  (Fig.  13) .  The  fruit  and 
foliage  of  many  varieties  some  weeks  after  revealed  a  large  increase 
in  the  disease  even  on  mature  apples.  The  infections  for  this  period 
were  even  greater  than  those  of  May  9  to  11. 

The  month  of  July  was  dry  with  the  exception  of  a  precipitation 
of  .68  of  an  inch  on  July  10.  The  month  of  August  was  characterized 
by  heavy  rainfall,  amounting  to  7.58  inches  near  Anna.  Healthy 
growths  exposed  from  June  28  and  July  8,  15  and  28  for  the  rest 
of  the  season  showed  disease  when  examined  on  September  7.  New 
lesions  of  the  disease  on  the  foliage  and  fruit  were  common  in  Illinois 
in  September  of  1921,  the  result  of  infections  favored  by  the  weather 
of  August.  The  data  do  not  reveal  to  what  extent  the  conditions  of 
July  10  were  favorable  for  infection  (it  is  probable  that  some  infec- 
tions occurred  at  this  date  at  Anna).  Heavy  infections  occurred  in 
August,  a  significant  fact  in  that  the  literature  so  far  has  always 
borne  testimony  against  the  probability  of  late  infections. 

Season  of  1922  at  Lilly  and  Other  Points. — In  this  season  the  writer 
had  opportunity  to  note  the  primary  period  of  infection  and  the  first 
appearance  of  the  disease  on  several  varieties  in  several  sections  of  the 
state.  The  bagging  experiment  was  conducted  on  Northwestern 


514 


BULLETIN   No.   256 


[February, 


Greening  trees  in  the  Lilly  orchards  (Table  10).    The  trees,  however, 
were  not  generally  diseased. 

Petal  fall  for  the  Northwestern  Greening  occurred  on  May  5  and  6 
and  the  first  bags  were  put  on  May  17,  eleven  days  after  petal  fall. 
The  bags  were  removed  at  intervals  from  May  29  to  July  20,  and  the 
growth  was  free  of  disease,  indicating  that  no  infection  occurred  on 
this  variety  at  Lilly  prior  to  May  17.  Growth  that  was  bagged 
on  May  29  and  June  1  and  examined  July  20  showed  disease,  indi- 
cating that  primary  infection  occurred  during  the  period  May  17  to 
May  29.  Heavy  rains  occurred  at  Lilly  during  the  period  May  23  to 


Sundar          I    :    Hcniay   •    I         Tuadav         I       YMntsday      /       Thursday       I          Wi 

wf?  ,»/,*  ,•;.«  •  ,w.^.v/,vf  ,»;£."?  •.•/.' "  ,*  >•*.•:  .v.v.1  ••  :,w;  .v.V.'r  vw 


Slauiay  I    •     Monday         1          Tuesday         [       VUHnaday       I        Tniirsaa. 

""  ''  «•«•«:.»•»•«««  "*  ••  >        '<«  •  »>*•  •  -**'•  «»•««        <  4 


FIG.  13. — THERMOGRAPH  AND  PRECIPITATION  RECORDS  IN  MILLER  ORCHARD, 
ANNA,  JUNE  18  TO  23,  1921 

Time  periods  for  Duchess  variety;    precipitation  for  twenty-four  hour 
period,  evening  to  evening. 

26,  approximately  two  and  one-half  weeks  after  petal  fall.  These 
dates  for  primary  blotch  infections  are  further  supported  by  the  fact 
that  the  first  symptoms  of  the  disease  were  apparent  on  June  7  to  8, 
or  fifteen  to  sixteen  days  later.  The  period  required  for  infection  to 
become  evident  agrees  closely  with  that  of  previous  years  for  other 
varieties  in  Illinois.  The  month  of  June  was  relatively  dry  and 
unfavorable  for  infection.  Of  eighteen  growths  protected  up  to  June 
8,  16,  and  July  1,  seven  were  diseased  when  examined  again  on  July 
20.  This  infection  was  associated  with  the  heavy  rains  of  July  1. 
Further  infections  occurred  later  in  the  summer.  Of  thirty-one 
growths  bagged  on  May  17  and  free  of  disease  on  July  20,  fifteen 
showed  symptoms  of  disease  on  October  15,  indicating  infection  periods 
after  July  20.  Because  of  the  small  number  of  cankers  on  these  trees, 


19S5] 


APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL 


515 


the  data  are  not  as  complete  as  would  be  expected  from  heavily  in- 
fected trees.  The  experiment,  however,  gave  valuable  information 
regarding  the  time  of  primary  infections  and  further  demonstrated 
the  fact  brought  out  in  previous  years  that  heavy  infections  occur 
under  ideal  conditions  as  late  as  August. 

Data  on  the  dates  of  primary  infection  and  the  appearance  of  the 
first  symptoms  were  also  obtained  from  Anna,  Olney,  Urbana,  Tonti, 
and  Hillview.  At  Urbana,  petal  fall  for  the  Duchess  variety  occurred 
on  May  3,  and  for  the  Ben  Davis  and  Northwestern  Greening  on 
May  5.  Blotch  first  appeared  on  the  fruit  and  leaves  of  the  Duchess 
variety  on  June  4  and  on  the  Northwestern  Greening  on  June  6. 

TABLE  10. — RESULTS  OF  BAGGING  EXPERIMENTS  ON   NORTHWESTERN  GREENING 
TREES,  LILLY  ORCHARDS,  LILLY,  1922. 


No.  of 
bags 

Date  put 
on 

Date  taken 
off 

Infection 

Second  examination 

Third  examination 

Date 

Infection 

Date 

Infection 

1 

May  17 

May  29 

— 

Oct.    15 

+ 

1 

" 

— 

July   20 

— 

Oct.    15 

M.f.  &  p.i. 

1 

— 

— 

S.f.  &  p.i. 

1 

— 

+ 

1 

4 

44 

— 

** 

— 

44 

1 

" 

— 

— 

1 

June    8 

— 

— 

+ 

1 

— 

Oct.    15 

— 

1 

" 

— 

July  20 

— 

44 

S.f.  &  p.i. 

1 

— 

11 

— 

Trace 

1 

June  16 

— 

" 

— 

M.p.i. 

1 

' 

" 

— 

" 

+ 

1 

" 

— 

S.f.  &  p.i. 

1 

— 

— 

1 

1 

" 

— 

" 

M.pi. 

1 

" 

— 

+ 

2 

July     1 

— 

— 

— 

1 

— 

— 

44 

S.p.i. 

2 

— 

M 

+ 

1 

.Oct.    15 

— 

2 

11 

— 

July  20 

+ 

1 

* 

*' 

— 

" 

— 

+ 

1 

" 

— 

— 

1 

July    10 

— 

Oct.    15 

— 

1 

1 

" 

— 

July   20 

— 

S.p.i. 

3 

— 

— 

2 

— 

41 

— 

+ 

1 

" 

— 

Oct.    15 

— 

1 

— 

S.p.i. 

1 

— 

July   20 

— 

S.p.i. 

5 

1 

July   20 

— 

Oct.    15 

— 

1 

— 

Trace 

3 

— 

" 

— 

8  (checks) 

Oct.    15 

— 

5 

May  29 

July  20 

+ 

1 

M.p.i. 

1 

— 

1 

+ 

Oct.    15 

+ 

4 

June     1 

" 

+ 

•'  ,'^ 

1 

" 

— 

— 

6 

June    8 

" 

+ 

1 

" 

" 

M.p.i. 

1 

Oct.    15 

S.f.  &p.i. 

1 

June  16 

July   20 

— 

44 

S.f.  &  p.i. 

6 

+ 

( —  )  =  disease  not  present ;  S.p.i.  =  severe  petiole  infection ;  M.p.i.  —  moder- 
ate petiole  infection;  S.f .  &  p.i.  •=.  severe  fruit  and  petiole  infection;  (-)-)  —  dis- 
ease present  but  degree  not  determined;  M.f .  &  p.i.  •=.  moderate  fruit  and  petiole 
infection. 


516  BULLETIN   No.   256  [February, 

It  was  first  found  on  the  Ben  Davis,  on  June  8.  The  heaviest  pre- 
cipitation of  the  month  of  May  occurred  on  May  25  and  26  (Fig.  14). 
The  first  infections  of  the  season  at  Urbana  also  occurred  at  this  time, 
or  about  three  weeks  after  petal  fall.  Precipitations  occurred  fre- 
quently in  the  middle  and  early  part  of  May,  but  since  they  were 
slight,  conditions  were  unfavorable  for  infection;  no  precipitation 
occurred  later  in  May. 

The  data  from  Anna  are  interesting  and  confirm  the  results  of  the 
previous  seasons.  The  period  of  petal  fall  and  of  the  calyx  spray 
was  April  17  to  20.  Blotch  was  found  on  Yellow  Transparent, 
Duchess,  and  Benoni  for  the  first  time  in  the  period  May  16  to  18, 
approximately  four  weeks  after  petal  fall.  Heavy  rains  occurred  at 
Anna  during  the  periods  April  25  to  28  and  May  2  and  3,  and  the 
conditions  were  ideal  for  infection,  but  the  conditions  in  the  latter 
period  were  responsible  for  the  first  infections  as  revealed  by  the 


PRECIPITATION          .01  .10  1.76  .34 


FIG.  14. — THERMOGRAPH  AND  PRECIPITATION  EECORDS  IN  UNIVERSITY 

ORCHARD,  URBANA,  MAY  22  TO  28,  1922 
Precipitation  for  twenty-four  hour  period,  morning  to  morning. 

results  from  several  demonstration  orchards  for  blotch  control  in 
Union  county  for  the  season  of  1922.  Eight  orchards  were  selected 
and  the  spraying  schedule  called  for  applications  at  intervals  of 
two,  three,  four,  and  six  weeks  after  petal  fall.  This  work  was 
supervised  by  the  assistant  farm  adviser  in  cooperation  with  the 
growers.  In  seven  of  these  orchards  the  two-weeks  spray  was  applied 
by  May  2,  but  in  the  remaining  orchard  difficulty  was  encountered  and 
the  two-weeks  spray  was  not  applied  until  after  the  rainy  period,  with 
the  result  that  the  fruit  and  foliage  of  this  orchard  were  heavily  in- 
fected, while  in  the  other  seven  orchards  control  was  excellent.  In 
the  Miller  orchard  at  Anna,  the  application  of  the  two-weeks  spray 
in  the  Benoni  orchard  was  interfered  with  by  rains  of  May  2  and  3, 
and  the  fruit  from  the  trees  which  failed  to  get  this  application  on 
time  was  diseased,  while  the  fruit  from  trees  sprayed  before  this 
period  was  clean.  The  data  therefore  indicate  that  the  first  infections 
occurred  at  Anna  in  the  period  May  2  and  3,  or  approximately  two 


1925}  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  517 

weeks  after  petal  fall.  The  disease  was  noted  generally  for  the  first 
time  during  May  16  to  18,  or  approximately  two  weeks  after  primary 
infection  took  place. 

At  Olney  on  Ben  Davis,  petal  fall  occurred  April  18  and  19,  and 
the  disease  was  first  found  on  May  21  and  22.  Primary  infection  was 
traced  to  the  heavy  precipitation  of  May  3  and  4,  about  two  weeks 
after  petal  fall.  At  Tonti,  fifty  miles  west  of  Olney,  the  initial  blotches 
on  Ben  Davis,  Benoni,  Grimes  Golden,  and  Duchess  fruit  were  found 
May  20  to  22.  Petal  fall  for  these  varieties  occurred  on  April  25  and 
26.  At  Hillview,  blotch  was  found  on  late  varieties  for  the  first  time 
on  May  24  and  25 ;  petal  fall  was  recorded  for  April  22  and  23. 

The  evidence  obtained  from  three  years  of  field  work  shows  that 
primary  blotch  infections  did  not  occur  prior  to  two  weeks  after  petal 
fall.  It  is  certainly  possible  for  primary  infections  to  occur  earlier  in 
exceptional  seasons,  and  no  doubt  a  field  study  of  the  fungus  over  a 
period  of  years  will  bear  out  this  statement.  It  is  interesting  to  note 
that  in  southern  Pennsylvania  in  1922,  according  to  Walton  and 
Orton,105  primary  infection  of  the  fruit  occurred  earlier  than  two 
weeks  after  petal  fall.  The  results  from  this  study  also  show  that 
severe  cases  of  fruit  and  leaf  infection  may  occur  in  August  under 
conditions  existing  in  Illinois. 

Conditions  Associated  with  Natural  Infection 

The  pycnidia  do  not  swell  and  discharge  their  spores  unless  they 
are  moistened.  Study  of  the  weather  during  the  growing  season  has 
shown  that  heavy  precipitation  is  required  to  bring  about  infection, 
since  considerable  wetting  is  necessary  to  soften  the  pycnidia  suffici- 
ently to  lead  to  the  expulsion  of  the  spores,  and  to  maintain  moist 
conditions  a  sufficient  length  of  time  for  spore  germination.  The 
pycnidia  in  the  dead  inner  portions  of  the  canker  are  the  first  to- 
discharge  spores,  yet  these  may  retain  their  spores  until  late  in  the 
summer  notwithstanding  the  heavy  rains  earlier  in  the  season. 

Moisture  alone  is  insignificant  since  the  spores  cannot  germinate 
unless  the  temperature  is  favorable.  Mature  spores  germinate  early 
at  the  higher  temperatures,  that  is,  25°  C.  (77°  F.)  and  30°  C.  (86°  F.).. 
The  percentage  of  germination  is  ultimately  as  great  at  the  lower 
temperatures,  that  is,  15°  C.  (59°  F.)  and  20°  C.  (68°  F.)  altho  the 
rate  of  growth  of  the  germ  tubes  is  much  less.  It  is  safe  to  assume  that 
if  germination  occurs  normally  at  the  low  temperatures,  infection 
may  occur  also  at  these  temperatures  as  indicated  by  the  conditions 
associated  with  primary  infections.  In  the  past  three  seasons,  the 
primary  infections  have  occurred  during  prolonged  periods  of  mois- 
ture, accompanied  and  followed  by  low  temperatures,  and  the  sum- 
mer infections  in  shorter  periods  of  heavy  rains  and  high  temperature. 
Moist  conditions  during  the  night  resulting  from  rains  during  the 


518  BULLETIN   No.   256  [February, 

day  prolong  the  conditions  favorable  for  spore  germination  and  thus 
obviously  for  infection.  There  is  ample  evidence  that  light  rains  of 
short  duration,  even  with  warm  temperature  are  not  favorable  to 
infection. 

In  1920  at  Anna  the  earliest  infections  occurred  in  the  periods 
May  11  to  13  and  May  16  to  18.  The  weather  on  May  11  was  marked 
by  continuous  rains  which  were  particularly  heavy  early  in  the  after- 
noon. The  maximum  temperature  of  22.8°C.  (73°F.)  occurred  at 
5  p.  m.,  and  rain  continued  thruout  the  night,  and  until  8  a.  m.  of 
May  12  (Fig.  12).  May  12  was  cloudy  from  8  to  11  a.  m.,  followed 
by  hot  sunshine,  with  thunder  showers  from  2  to  4  p.  m.  On  May 
13  the  weather  was  cloudy  and  windy,  the  temperature  was  low,  and 
rain  fell  again  in  the  evening.  For  three  days  prior  to  May  11  the 
temperature  was  near  26.6°C.  (80°F.)  at  midday,  and  the  weather 
was  fair  and  dry.  Repeated  examinations  of  the  pycnidia  during 
this  period  revealed  that  the  spores  were  mature.  The  wet  period 
of  twenty-eight  hours  from  noon  May  11  to  4  p.  m.  May  12  was  ideal 
for  spore  germination.  Low  temperatures  prevailed  during  the  period 
May  13  to  17,  cloudy  and  windy  weather  from  May  13  to  15,  and 
heavy  rains  on  May  16,  17,  and  18.  On  May  19  and  21  the  atmosphere 
was  very  humid,  high  temperatures  prevailed  at  midday,  and  rains 
and  thunder  showers  in  the  evenings.  The  precipitation  for!  the 
period  May  11  to  21  amounted  to  6.13  inches.  Prolonged  wet  weather 
of  this  kind  is  common  in  Illinois  in  the  latter  part  of  April  and  in 
May  before  the  dry  season  begins. 

The  bagging  results  for  1920  on  the  Duchess  variety  at  Anna  show 
that  further  infection  occurred  in  the  period  from  May  30  to  June  4 
(Fig.  12).  The  weather  for  this  period  was  as  follows:  thunder 
showers  early  in  the  morning  of  May  30,  rain  all  day,  amounting  to 
.78  of  an  inch  with  intermittent  periods  of  warm,  bright  sunshine, 
thunder  showers  at  night  and  early  in  the  morning  of  May  31,  fol- 
lowed by  clear  weather  and  high  temperatures  for  the  day;  cloudy 
on  June  1  and  2,  with  high  humidity ;  thunder  showers  in  the  evening 
of  June  2  and  rain  all  day  on  June  3,  continuing  until  11  p.  m., 
and  amounting  to  1.54  inches ;  cloudy  and  high  humidity  on  June  4. 
For  one  week  prior  to  this  period,  and  two  weeks  after,  the  weather 
was  fair  and  dry. 

The  conditions  associated  with  the  first  heavy  infections  in  1921  at 
Anna  in  the  period  May  9  to  12  were  similar  to  those  of  the  preceding 
year  (Fig.  13).  The  precipitation  during  this  period  amounted  to 
1.58  inches,  the  days  were  cloudy  and  foggy,  and  the  rains  were  pro- 
longed and  drizzly,  interrupted  by  heavy  showers.  There  was  no 
sunshine  during  the  entire  period  and  the  temperature  was  compara- 
tively low.  For  almost  two  weeks  prior  to  May  9  the  weather  wa? 
relatively  dry  and  clear.  After  May  12,  no  rain  occurred  until  May 


1925}  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  519 

27.  Blotch  was  found  on  the  fruit  and  foliage  on  May  28,  as  a  result 
of  the  infection  of  this  period,  and  was  also  found  generally  distrib- 
uted in  the  county. 

Extensive  infections  occurred  on  June  19,  1921,  at  Anna  during 
heavy  thunder  showers  from  7  a.  m.  to  3  p.  m.  (Fig.  13).  The  rain 
was  forceful  and  amounted  to  3  inches  within  the  period  of  eight 
hours,  thus  drenching  the  orchard  so  thoroly  that  the  leaves  remained 
wet  thruout  the  night.  The  temperature  rose  from  21.1°C.  (70°F.) 
when  the  showers  began,  to  33.3°C.  (92°F.)  at  2  p.  m.,  and  remained 
above  21.1°C.  (70°F.)  for  sixteen  hours,  that  is,  from  8  a.  m.  to 
12  p.  m.  Both  moisture  and  temperature,  therefore,  were  favorable 
for  rapid  and  early  spore  germination.  The  extensive  infections  of 
this  period  wrere  evident  about  two  weeks  later.  For  many  days  pre- 
ceding the  thunder  showers  of  May  19  the  weather  was  clear,  and  for 
many  days  after  it  was  dry,  except  for  traces  of  rain  on  June  23,  24, 
and  25.  The  conditions  of  June  19  demonstrated  the  fact  that  with 
high  temperature  and  heavy  rain,  infection  occurs  in  a  shorter  time 
than  in  the  spring  when  the  temperature  is  low. 

In  the  season  of  1922  at  Urbana  heavy  infections  occurred  during 
the  wet  period  of  May  25  and  26  (Fig.  14).  The  weather  conditions 
during  this  period  were  as  follows:  continuous  rains  on  May  25, 
.amounting  to  1.76  inches  for  the  twenty-four  hour  period  from  7  a.  m. 
May  25  to  7  a.  m.  May  26,  cloudy  in  the  evening  of  May  25  and  moist 
conditions  thruout  the  night ;  cloudy  weather  on  May  26  with  occa- 
sional rains  amounting  to  .34  of  an  inch.  On  both  days  there  were 
thunder  showers  and  the  weather  was  continuously  moist,  while  the 
temperature  was  never  below  15.5°  C.  (60°  P.).  The  heavy  precipita- 
tion was  ideal  for  infection,  which  was  generally  apparent  on  all 
susceptible  varieties  by  June  9. 

The  rains  and  wet  periods  of  the  types  described  for  May  and 
June  are  responsible  usually  for  the  heaviest  infections  of  the  season. 
It  is  obvious,  then,  that  sprays  must  be  applied  frequently  in  this  season 
of  the  year.  In  the  summer  months  the  frequency  of  infection  is  less 
in  the  dry  period  which  often  extends  thru  the  entire  summer ;  con- 
sequently, spraying  in  this  period  for  apple  blotch  is  necessary  only  at 
wide  intervals. 

Development  of  the  Fungus 

Pycnidial  Stage  (a)  in  the  Bark. — The  twig  growth  of  infected 
trees  reveals  in  August,  for  the  first  time  in  the  season,  small  purplish 
cankers,  particularly  noticeable  at  the  nodes,  and  sometimes  at  the 
internodes.  They  are  very  common  on  the  water  sprouts. 

Bark  cankers  are  the  result  of  two  different  modes  of  infection. 
First,  they  may  result  from  the  growth  of  the  fungus  from  the 
•diseased  basal  portion  of  the  petiole  across  the  absciss  layer  and  into 


520  BULLETIN   No.   256  [February,. 

the  cortex  of  the  twig.  The  majority  of  the  node  infections  occur  in 
this  manner.  Second,  they  may  result  directly  from  spore  infections. 
The  internode  cankers  are  the  results  of  such  infections. 

The  pycnosclerotia  appear  rapidly  with  the  enlargement  of  the 
canker,  and  their  growth  in  size  causes  the  rupture  of  the  epidermis, 
and  their  exposure.  Many,  however,  are  not  exposed  until  the  follow- 
ing spring. 

In  Illinois  the  conditions  in  August  and  September  are  favorable 
for  the  growth  of  the  fungus.  These  conditions  prevail  only  for  a 
short  time,  for  usually  in  the  latter  part  of  September  and  early  in 
October  growth  ceases,  and  the  cankers  remain  nearly  dormant  thru- 
out  the  winter.  The  inhibition  of  the  fungus  during  the  winter  months 
is  due  to  the  prevailing  low  temperature  and  to  the  presence  of  an 
absciss  layer  of  cells  inside  of  the  diseased  region. 

In  March  of  the  following  year,  the  interior  cells  of  the  pycnosclero- 
tium  begin  to  differentiate  and  spores  appear  in  the  center.  Spore 
formation  continues  until  all  of  the  pseudo-parenchyma  context  has 
become  differentiated.  First,  a  distinct  sporogenous  layer  appears 
lining  the  small  central  cavity;  this  increases  in  size  as  the  sporo- 
genous layer  progresses  outward  to  the  dense  dothideaceous  membrane. 
The  conidiophores  are  of  various  lengths  and  frequently  distinctly 
septate.  The  spores  are  produced  acrogenously,  each  cell  below  the 
ejected  spore  giving  rise  to  another  spore.  The  pseudo-parenchyma 
context  is  gelatinous  and  in  the  process  of  spore  formation  some  of  the 
gelatinous  substance  is  retained  on  the  broad  pole  of  the  spore  in  the 
form  of  an  appendage,  but  is  dissolved  with  the  maturity  and  germina- 
tion of  the  spores  (Fig.  9Ai). 

Early  in  April,  the  vegetative  growth  of  the  fungus  in  the  canker 
is  resumed  and  the  cankers  increase  rapidly  in  size.  The  formation 
of  new  cankerous  areas  about  the  original  canker  continues  actively 
thruout  April  and  early  May.  With  warm,  dry  weather,  and  with 
the  formation  of  absciss  layers  by  the  host,  the  progress  of  the  fungus, 
is  inhibited  again,  and  the  cankers  remain  relatively  quiescent  during 
the  summer  months.  Simultaneously  with  the  enlargement  of  the 
canker,  true  pycnidia  appear  over  the  surface.  There  are  present  in 
the  canker  at  the  beginning  of  the  season,  therefore,  two  distinct 
sources  of  spores,  first,  the  pycnosclerotia  of  the  original  canker,  and 
second,  the  pycnidia  formed  with  the  advance  of  the  canker. 

With  age  the  older  portions  of  the  canker  become  hard  and  dry, 
and  rifting  and  exfoliation  of  the  bark  occurs.  The  canker  becomes 
marked  by  definite  growth  areas  and  the  tissues  become  dessicated 
and  cracked.  After  the  pycnidia  have  discharged  their  spores,  the 
cankers  become  occupied  by  saprophytic  fungi,  notably  of  the  genera 
Phoma  and  Septoria.  Under  the  dead  exfoliating  bark,  the  periderm 


APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL 


521 


layer,  formed  in  advance  of  the  fungus,  develops  to  the  extent  of 
starving  the  fungus  and  repairing  the  wound. 

In  August  and  September  the  fungus  grows  rapidly,  and  simultane- 
ously produces  pycnosclerotia.  New  cankers  now  appear  for  the 
first  time  in  the  season  and  bear  only  pycnosclerotia.  They  appear 
to  be  the  result  of  the  same  inocula  which  cause  infection  of  the  fruit 
and  foliage,  the  incubation  period  being  unusually  long. 

The  fungus  grows  year  after  year  in  the  bark,  causes  the  increased 
annual  enlargement  of  the  cankers,  and  produces  pycnidia  in  the 
spring  and  summer,  and  pycnosclerotia  late  in  the  summer.  Growth, 

TABLE  11. — ISOLATIONS  OF  P.  solitaria  FROM  BRANCHES  OF  DUCHESS  VARIETY 
Two  TO  FIVE  YEARS  OLD 


Pure  cultures, 
successful 

Contaminated  cultures, 
unsuccessful 

Total  number  of 
cultures 

Two-year  wood  
Three-year  wood  

edge  .... 
/edge.... 

3 
3 

4 
2 

7 
5 

Four-year  wood  

(.center.  .  . 
(edge  

3 

4 

1 
3 

4 

7 

Five-year  wood  

'  '  \center.  .  . 
/edge.  .  .  . 

4 
5 

1 

2 

5 

7 

'  '  (center.  .  . 

0 

7 

7 

however,  is  much  slower  after  the  first  year  and  the  rate  decreases 
with  age.  Previous  investigators  of  apple  blotch  concede  that  the 
fungus  is  inhibited  in  its  growth  within  three  or  four  years  and  that 
the  cankers  disappear  at  the  end  of  this  period.  This  may  be  true 
for  some  varieties  and  under  certain  conditions,  but  it  is  not  true 
generally  for  all  varieties.  The  fungus  may  live  indefinitely  in  the 
bark. 

In  order  to  establish  proof  of  the  longevity  of  the  organism  in  the 
bark,  isolations  were  made  both  from  the  advancing  and  the  central 
portions  of  cankers  from  Duchess  trees. 

Table  11  shows  the  results  of  isolations  from  cankers  on  Duchess 
branches  made  February,  1921.  The  bark  varied  in  age  from  two 
to  five  years.  The  unsuccessful  cultures  bore  saprophytes.  These 
saprophytes  exist  largely  in  the  dead  central  portions  of  the  cankers, 
but  may  also  occur  in  the  raised  marginal  living  tissue  of  the  canker. 
In  March,  1921,  isolations  were  again  made  from  cankers  on  Duchess 
branches  with  the  results  presented  in  Table  12. 

Later  in  March  further  isolations  were  made  from  edges  and 
centers  of  cankers  on  twelve-year-old  bark.  Of  nine  isolations  from 
the  central  areas,  two  gave  pure  cultures,  and  of  thirteen  isolations 
from  the  edge,  six  gave  pure  cultures. 

These  facts  demonstrate  that  the  fungus  may  continue  its  per- 
ennial habit  in  the  bark  for  many  years  on  this  variety.  Other  varie- 


522 


BULLETIN  No.  256 


[February, 


ties  very  susceptible  to  bark  infection  likewise  manifest  the  long- 
lived  character  of  the  fungus,  i.e.,  the  Benoni,  Chenango,  North- 
western Greening,  and  Missouri  Pippin.  Other  less  susceptible  varie- 
ties like  the  Ben  Davis,  Yellow  Transparent,  and  Rome  Beauty,  may 
support  the  fungus  for  only  three  or  four  years. 

(b)  In  the  Fruit. — The  infections  responsible  for  the  initial 
blotches  usually  occur  in  May,  ordinarily  between  two  and  three  weeks 
after  petal  fall,  tho  they  may  occur  even  five  weeks  afterwards.  In 
some  years  they  may  occur  in  the  latter  part  of  April,  as  in  1921. 


TABLE  12.- 


-ISOLATIONS  OF  P.  solitaria  FROM  BRANCHES  OF  DUCHESS  VARIETY 
FOUR  TO  EIGHT  YEARS  OLD 


Pure  cultures, 
successful 

Contaminated  cultures, 
unsuccessful 

Total  number  of 
cultures 

Four-year  wood  

f  edge  .... 

3 

3,  > 

6 

Five-year  wood  

'  '  \center.  .  . 
/edge.... 

0 
3 

3 
3 

3 

6 

Six-year  wood  

\center.  .  . 
/edge.... 

3 
3 

3 
3 

6 
6 

Seven-year  wood  

\center.  .  . 
f  edge  .... 

3 
2 

3 
4 

6 
6 

Eight-year  wood  

'  '  '  '  \center.  .  . 
/edge.... 

1 
4 

5 
2 

6 
6 

\center.  .  . 

0 

6 

6 

Symptoms  appear  two  to  three  weeks  after  initial  infection.  The  in- 
cubation period  of  the  disease  on  the  apple  may  vary  according  to 
climatic  conditions  and  in  some  seasons  may  be  shorter  for  early 
varieties,  such  as  Duchess  and  Yellow  Transparent,  than  for  late 
varieties  such  as  Ben  Davis. 

The  pycnidia  are  usually  present  on  the  first  appearance  of  the 
blotches,  at  first  sparse  and  then  many,  but  always  definite  and  dis- 
tinct. The  pycnospores  are  produced  rapidly  and  microscopic  ex- 
amination shows  that  they  are  present  simultaneously  with  the  ap- 
pearance of  the  pycnidia.  Usually  within  ten  days  after  the  first 
evidence  of  the  lesions,  the  pycnidia  are  black  and  upon  being  crushed 
emit  a  mass  of  loose,  distinct  and  apparently  mature  spores.  The 
rapidity  with  which  the  pycnidia  develop  and  form  spores  is  remark- 
able. Oozing  of  spores  from  these  pycnidia  occurs  in  June  and 
July,  under  favorable  conditions  leading  to  secondary  infections  of 
the  fruit  and  foliage. 

All  of  the  pycnidia  are  not  emptied  under  the  first  favorable 
conditions.  The  repeated  infection  of  the  new  growth  causes  much 
increase  in  the  disease  on  the  fruit  and  foliage,  which  later  serve  as 
sources  of  further  infections.  The  spores  from  the  pycnidia  on  the 
primary  blotches  may  reinfect  the  same  apple.  Examples  of  this  are 
common  in  the  summer.  The  new  lesions  are  small  and  numerous 
and  often  appear  directly  below  the  large  blotches. 


1925] 


APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL 


523 


The  blotches  increase  in  size  with  age.  Late  blotches  resulting 
from  late  infections  develop  slowly  and  usually  remain  small.  On 
early  maturing  varieties,  such  as  the  Duchess  and  Yellow  Transparent, 
the  blotches  are  small,  while  on  the  late  maturing  varieties,  such  as 
Ben  Davis,  Northwestern  Greening,  and  Rome  Beauty,  they  become 
quite  large.  As  the  blotches  develop,  the  affected  tissue  becomes  hard 
and  dry,  the  growth  of  the  underlying  tissue  is  stunted,  and  the 
tension  that  arises  from  growth  of  the  surrounding  tissues  results 


FIG.  15. — SECTION  THRU  PYCNOSCLEROTIA  FROM  APPLE  IN  COLD 
STORAGE,  FEBRUARY  10,  1920 

in  the  cracking  of  the  apple  across  the  lesion.  On  the  early  ma- 
turing varieties  the  cracks  are  usually  small,  narrow,  or  absent,  but 
on  later  maturing  varieties  they  are  quite  large  and  deep.  Pycnidia 
commonly  form  inside  the  cracks  on  the  fleshy  pulp. 

The  blotches  increase  in  size  and  produce  pycnidia  as  the  apple 
develops.  In  August  only  pycnosclerotia  are  formed;  the  pycnidia 
formed  previous  to  August  also  become  pycnosclerotia  by  the  rejuvena- 
tion of  the  sporogenous  layer.  Their  walls  become  thick,  carbonaceous, 
and  the  pycnosclerotia  sometimes  coalesce  and  become  somewhat 
stromatic  (Fig.  15).  No  pycnidia  with  spores,  therefore,  are  present 
on  the  blotches  after  September.  Early  in  the  following  spring  the 
pseudo-parenchyma  cells  of  the  pycnosclerotia  differentiate  and  by 
April  or  May  many  of  the  pycnosclerotia  contain  distinct  and  appar- 
ently mature  pycnospores.  Attempts  to  germinate  the  pycnospores 
obtained  from  these  sources  were  generally  unsuccessful. 


524  BULLETIN   No.   256  [February, 

(c)  In  the  Foliage. — The  disease  is  apparent  two  to  three  weeks 
after  infection.  Pycnidia  with  spores  appear  very  early  and  can  be 
recognized  on  the  youngest  lesions,  maturing  within  a  few  days. 
In  Illinois  under  favorable  conditions  these  pycnospores  are  liberated 
in  June,  resulting  in  new  infections  of  the  fruit  and  leaves ;  these, 
then  serve  as  additional  sources  of  inoculum.  After  the  spores  are 
expelled,  the  pycnidia  cease  functioning.  The  lesions  resulting  from 
late  infections  both  on  the  blades  and  petioles  bear  pycnosclerotia  as 
on  the  fruit  and  pass  the  winter  in  this  resting  stage  and  usually 
produce  pycnospores  the  following  spring.  Pycnosclerotia  from  over- 
wintered foliage  have  been  examined  in  the  spring  and  frequently 
pycnospores  have  been  found.  Pycnosclerotia  are  more  common  on 
the  petioles  than  on  the  blades,  because  the  growth  of  the  fungus  011 
the  petioles  continues  late  in  the  season. 

The  development  of  the  disease  on  the  petioles  offers  a  serious 
aspect.  At  first  the  petiole  canker  is  small. and  ellipitical,  and  during 
the  course  of  the  season  the  fungus  grows  downward  across  the  leaf 
scar  into  the  cortex  of  the  twig,  usually  girdling  the  petiole.  As 
early  as  1909  Scott  and  Rorer79  were  aware  of  the  serious  aspect  of 
petiole  infection.  The  significance  of  these  petiole  lesions  was  again 
emphasized  by  Gardner,35  who  thus  explained  the  occurrence  of  so 
high  a  percentage  of  cankers  at  the  nodes. 

The  initial  lesions  on  the  petioles  commonly  occur  on  the  lower 
side.  Growth  is  rapid  at  first  and  usually  by  August,  particularly  if 
infection  occurs  at  the  base  of  the  petiole,  the  fungus  has  extended 
across  the  absciss  layer,  and  by  the  latter  part  of  August  or  early 
in  September  the  canker  is  evident,  usually  adjacent  to  the  bud. 
Frequently  the  hyphae  do  not  cross  the  absciss  layer  until  late  in  the 
season  and  the  infection  at  the  node  is  not  evident  until  the  following 
spring.  The  mycelium  may  grow  downward  within  the  petiole  and 
across  the  absciss  layer  before  the  leaf  falls.  Not  all  cankers  about 
the  nodes  are  the  result  of  these  basal  petiole  infections.  The  axil  of 
the  leaf  furnishes  a  convenient  place  for  lodging  spores  and  water 
and  thus  for  infection,  resulting  in  frequent  infection  of  the  bud 
scales,  and  the  direct  infection  of  the  bark  of  the  twig  around  the 
bud.  In  Illinois  75  to  90  percent  of  the  bark  cankers  are  the  result 
of  node  infections,  resulting  either  from  the  direct  infection  of  the 
bark,  or  indirectly  by  the  vegetative  growth  of  the  fungus  from  the 
infected  bud  scales,  buds,  and  petioles. 

Serious  petiole  infection  causes  early  leaf  fall.  In  the  season  of 
1921,  in  the  general  absence  of  a  crop,  no  spraying  was  done  for 
blotch,  and  petiole  infection  was  severe.  In  southern  Illinois,  on  the 
Duchess  variety,  girdling  of  the  petioles  was  completed  in  late  July 


1925}  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  525 

and  early  in  August  and  the  lower  branches  of  the  trees  were  con- 
spicuously defoliated  by  the  latter  part  of  August. 

Ascigerous  Stage. — The  morphology,  development,  and  life  history 
of  P.  solitaria  and  of  the  imperfect  stage  of  Guignardia  bidwellii  show 
many  interesting  analogies. 

In  the  development  of  black  rot  of  grape,  as  reported  by  Reddick,66 
the  pycnospores  are  produced  in  large  numbers  on  the  mummied 
berries  from  June  until  early  August.  They  are  discharged  under 
favorable  conditions  and  may  produce  new  infections.  In  August, 
pycnosclerotia  and  spermogonia  are  produced  on  the  new  spots  on  the 
berries.  Early  in  the  spring  some  of  these  pycnosclerotia  become 
perithecia,  and  others,  true  pycnidia.  The  simultaneous  production 
of  pycnosclerotia  and  spermogonia  indicates  the  approach  of  the 
ascigerous  stage. 

In  the  development  of  P.  solitaria  on  the  leaves,  only  the  late 
appearing  lesions  bear  pycnosclerotia ;  the  pycnidia  which  formed  and 
functioned  earlier  in  the  season  on  early  lesions  terminate  their  ex- 
istence after  the  pycnospores  are  discharged.  On  the.  fruit,  pycnos- 
clerotia are  likewise  present  on  late  appearing  blotches;  but  the 
pycnidia  formed  early  in  the  season  on  blotches  also  become  pycnos- 
clerotia after  spore  discharge  and  pass  the  winter  in  this  resting 
condition.  All  the  fruiting  bodies  on  the  apple,  therefore,  pass  the 
winter  as  pycnosclerotia  (Fig.  15).  A  similar  development  has  been 
reported  for  black  rot  on  the  grape  berry  by  Prillieux,61  Jaczewski,49 
Perraud,60  and  Prunet.62  They  report  that  pycnidia  on  the  fruit  pass 
into  the  resting  stage  in  the  autumn,  and  that  the  ascigerous  stage 
may  follow  during  the  next  spring.  Quoting  from  Jaczewski : 

"When  grapes  affected  with  black  rot  are  dried  or  exposed  to  a 
low  temperature  (8°  to  10°  C.),  the  formation  of  stylospores  ceases 
completely  and  the  pycnidia  fill  up  with  a  white  compact  pulp  which 
consists  of  polygonal  cells  very  rich  in  oil  drops.  The  over-wintering, 
resting  pycnidia,  when  exposed  to  the  moist  weather  of  the  spring, 
differentiate  again.  In  them,  there  develops  a  new  activity  of  the 
pulp  cells  which  leads  to  the  formation  of  ascospores.  The  pycnidia 
therefore  become,  in  this  way,  perithecia.  It  must  be  noted  that  all 
of  the  perithecia  do  not  reach  their  full  development  and  Prunet  has 
already  observed  that  the  resting  pycnidia  (so-called  sclerotia)  in 
nature,  transform  more  readily  into  pycnidia  with  stylospores  than 
into  perithecia." 

The  development  is  similar  to  P.  solitaria  on  the  fruit  and,  altho 
no  ascigerous  stage  has  yet  been  found,  the  indication  is  that  its 
occurrence  and  formation  is  like  that  of  the  black  rot  fungus. 

In  the  spring  many  of  the  pycnosclerotia  of  P.  solitaria  form 
pycnospores  and  many  remain  sterile.  Attempts  by  the  writer  to 


526 


BULLETIN   No.   256 


[February? 


discover  the  ascigerous  stage  among  overwintering  fruit  and  leaves 
have  been  unsuccessful  altho  doubtless  it  may  eventually  be  found  as 
one  of  the  final  stages  of  the  pycnosclerotium. 

VARIETAL  SUSCEPTIBILITY 

The  relative  susceptibility  of  varieties  of  Malus  Malus  to  apple 
blotch  has  been  measured  in  the  past  largely  by  the  severity  and  pre- 
valence of  the  disease  on  the  fruit.  This  method,  however,  does  not 
measure  the  relative  susceptibility  of  varieties  nor  the  amount  and 
severity  of  the  disease  on  the  bark  since  the  bark  shows  a  much 
wider  variation  to  infection  than  the  fruit.  The  comparative  sus- 
ceptibility of  the  bark  is  more  significant  also  because  the  amount  of 
infection  on  the  fruit  depends  on  the  prevalence ,  and  distribution  of 
the  cankers  on  the  tree.  The  Jonathan  variety  is  a  typical  example, 
the  bark  of  which  is  resistant  under  Illinois  conditions.  When  this 
variety  grows  at  a  distance  from  infected  Duchess  or  Ben  Davis 
trees  for  example,  spraying  for  blotch  is  unnecessary,  but  growing 

TABLE  13. — RELATIVE  SUSCEPTIBILITY  OF  APPLE  FRUIT  TO  Phyllostwta  solitaria 


Very  Susceptible 


Arkansas  Black 

Gilpin 

Paradise  Sweet 

Arkansas  Red 

Harvest  Pippin 

Red  Astrachan 

Ben  Davis 

Hawthornden 

Rhode  Island  Greening 

Benoni 

Huntsman  Favorite 

Rome  Beauty 

Bentley  Sweet 

Krauser 

Royal  Pearmain 

Chenango 

Lansingburg 

Schockley 

Clayton 

Lawver 

Smith  Cider 

Doraine 

Limbertwig 

Sops  of  Wine 

Duchess 

Maiden  Blush 

Stark 

Early  Harvest 

Mann 

Tolman  Sweet 

Ewait 

Missouri  Pippin 

Wagener 

Fameuse 

Northwestern   Greening 

White  Winter  Pearmain 

Gano 

Oliver  (Senator) 

Yellow  Transparent 

Moderately  Susceptible 


Aiken  Red 

Baldwin 

Bradford 

Champion 

Fink 

Golden  Russet 

Ingram 


Mammoth  Black  Tv.ig 

May  of  Myers 

McAfee 

Mclntosh 

Minkler 

Northern  Spy 

Rails  Gennett 


Rrunbo 
Roman   Stem 
Salome 
Shannon 
Willow  Twig 
Yellow  Bellflower 
Yellow  Newton 


Resistant  or  Slightly  Susceptible 


Delicious 
Grimes  Golden 


Jonathan 
Red  June 


Stayman  Winesap 
Wealthy 


York  Imperial 
Winesap 


1925]  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  527 

adjacent  to  such  susceptible  varieties  the  fruit  of  the  Jonathan  be- 
comes infected. 

The  fruit  of  practically  all  the  important  commercial  varieties 
of  apples  in  Illinois  is  susceptible.  Observations  indicate  that  the 
Winesap  variety  as  a  whole  is  resistant,  yet  the  fruit  of  this  variety 
may  be  found  infected  under  favorable  conditions  as  is  true  of  the 
fruit  of  many  other  varieties  whose  bark  is  resistant,  such  as,  Sops 
of  Wine,  May  of  Myers  (Rheinish  May),  Wealthy,  Jonathan,  Early 
Harvest,  York  Imperial,  and  Grimes  Golden.  Lewis51  found  under 
Kansas  conditions  that  the  Winesap  and  York  Imperial  are  most 
resistant  but  that  occasionally  the  fruit  becomes  infected. 

In  an  orchard  near  Anna,  several  Benoni  trees  are  partly  top- 
worked  with  the  Miller  variety.  In  the  absence  of  sprays,  the  apples 
on  the  trees  become  infected  and  there  seems  to  be  no  wide  difference 
in  the  susceptibility  of  these  two  varieties  of  apples.  Only  the  Benoni 

TABLE  14. — RELATIVE  SUSCEPTIBILITY  OF  APPLE  BAKK  TO  Phyllosticta  solitaria 

Very  Susceptible 


Benoni 
Bentley  Sweet 
Chenango 

Duchess 
Fameuse 
Lawyer 
Mann 

Missouri  Pippin 
Northwestern  Greening 
Smith  Cider 

Moderately  Susceptible 


Baldwin 
Ben  Davis 
Gano 
Limbertwig 

Maiden  Blush 
Mclntosh 
Oliver  (Senator) 
Red  Astrachan 

Rhode  Island  Greening 
Rome  Beauty 
Stark 
Yellow  Transparent 

Resistant  or  Slightly  Susceptible 


Aiken  Red 

Ingram 

Red  June 

Champion 

Jonathan 

Sops  of  Wine 

Delicious 

Mammoth  Black  Twig 

Stayman  Winesap 

Early  Harvest 

May  of  Myers 

Wealthy 

Fallawater 

Minkler 

Willow  Twig 

Fink 

Northern  Spy 

Winesap 

Grimes  Golden 

Rails  Genett 

Yellow  Newton 

Huntsman 

Rambo 

York  Imperial 

Susceptible  to  Bark  Infection  but  Degree  of  Susceptibility  Doubtful 

Arkansas  Black  Golden  Russet  Salome 

Arkansas  Red  Harvest  Pippin  Schockley 

Bradford  Hawthornden  Shannon 

Clayton  Lansingburg  Tolman  Sweet 

Domine  McAfee  Wagener 

Gilpin  Roman  Stem  White  Winter  Peru-main 
Royal   Pearmaiu 


528  BULLETIN   No.   256  [February, 

twigs  and  branches,  however,  were  cankered.  The  fruit  of  the  Miller 
trees  located  at  a  distance  from  Benoni  trees  was  always  free  of 
blotch  even  when  unsprayed.  Similarly  Adams1  in  Pennsylvania  re- 
ports an  instance  where  Smith  Cider  was  extremely  susceptible  to 
canker  infection  while  Grimes  Golden  growing  adjacent  was  but 
slightly  infected  and  on  the  York  Imperial  it  was  impossible  to  find 
cankers.  The  fruit  of  the  last  two  varieties,  however,  was  badly 
infected.  These  and  other  observations  warrant  the  statement  that 
the  infection  of  the  fruit  of  any  variety  is  directly  associated  with 
its  proximity  to  infected  bark.  It  seems  then  that  in  selecting  varieties 
for  the  orchard,  the  susceptibility  of  the  bark  rather  than  of  the 
fruit  is  worthy  of  most  consideration.  Planting  of  susceptible  varieties 
of  high  commercial  value  may  be  recommended,  but  their  location  in 
relation  to  bark  resistant  varieties  should  be  planned  carefully. 

A  limited  number  of  varieties  in  Illinois  are  seriously  susceptible 
to  bark  infections.  About  an  equal  number  are  moderately  so,  while 
the  majority  are  resistant  or  only  slightly  susceptible.  The  Duchess, 
Smith  Cider,  Northwestern  Greening,  and  Missouri  Pippin  are  ex- 
amples of  varieties  whose  fruit  and  bark  are  extremely  susceptible. 
The  fruit  of  the  Yellow  Transparent  is  very  susceptible  but  to  a 
less  degree  than  the  fruit  of  the  Smith  Cider  and  Ben  Davis.  The 
bark  of  the  Ben  Davis  is  more  susceptible  than  the  bark  of  the  Yellow 
Transparent  and  frequently  the  latter  is  quite  resistant.  The  fruit 
of  the  Rome  Beauty  is  very  susceptible,  but  according  to  the  suscep- 
tibility of  the  bark  this  variety  is  in  the  class  with  the  Ben  Davis. 
The  Jonathan,  Grimes  Golden,  and  York  Imperial  varieties  might 
be  classified  alike  because  of  the  resistance  of  the  bark  and  because 
the  fruit  is  less  than  moderately  susceptible.  The  variations  in  the 
susceptibility  of  the  fruit  and  bark  in  different  localities  prevent 
satisfactory  separation  of  varieties  into  more  than  three  classes  of 
susceptibility.  (Tables  13  and  14.) 

DISSEMINATION 

When  bark-resistant  and  bark-susceptible  varieties  are  growing 
in  adjacent  rows  the  fruit  of  the  bark-resistant  varieties  becomes  in- 
fected usually  only  on  the  side  exposed  to  the  infected  trees  and  within 
the  drip  of  the  infected  branches.  This  indicates  that  the  dissemina- 
tion of  spores  is  limited  to  a  comparatively  short  distance  during 
periods  when  conditions  are  favorable  for  infection.  The  constant 
proximity  of  the  fruit  and  foliage  lesions  to  the  cankers  on  the  same 
tree  also  indicates  that  the  infectious  material  is  carried  only  a 
relatively  short  distance  under  these  conditions.  The  washing  rains 
associated  with  infection  carry  the  spores  downward  to  the  lower  half 


1925]  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  529 

of  the  tree  as  is  always  evidenced  by  the  relative  absence  of  the  disease 
high  up  on  the  tree  and  the  abundance  of  it  on  the  lower  branches. 
The  splashing  rains  and  washings  assisted  by  wind  carry  the  fungus 
into  the  adjacent  rows. 

In  Knox  county,  in  September,  1921,  the  disease  was  found  con- 
fined to  a  few  trees  in  a  block  of  Northwestern  Greening  and  the  ex- 
amination of  the  twigs  showed  that  a  few  isolated  cankers  were  pres- 
ent on  the  preceding  season's  growth.  A  similar  instance  was  found 
in  the  same  season  at  Mount  Morris,  Ogle  county,  on  a  single  tree  in 
the  center  of  a  block  of  twenty-year-old  Northwestern  Greening.  A 
thoro  examination  of  the  orchard  revealed  a  single  canker.  "  Both  of 
the  above  orchards  are  located  in  counties  where  serious  isolated  cases 
of  the  disease  are  known. 

The  spores,  which  are  extruded  in  gelatinous  masses,  may  retain 
their  vitality  for  some  time  and  dried  fragments  of  the  exudate  and 
individual  spores  may  be  carried  by  wind  currents  for  some  distance. 
Ordinarily,  pycnospores  are  short-lived,  but  in  the  case  of  PJioma 
uvicola,  a  very  closely  related  organism,  according  to  Scribner80  the 
pycnospores  may  germinate  after  six  months  under  dry  conditions. 
According  to  Rathay65  the  dissemination  of  the  pycnospores  of  the 
black-rot  fungus  is  effected  by  water  and  wind,  the  former  freeing 
the  binding  substance  of  the  cirrhi.  Viala,  according  to  Rathay65 
(p.  311),  observed  that  on. continued  drjdng  the  slimy  cirrhi  shrivel 
and  crumble  away  and  that  the  wind  blows  away  small  fragments 
holding  three  to  four  pycnospores.  The  dissemination  of  the  spores 
of  P.  solitaria  under  dry  conditions  by  the  wind,  as  the  above  authors 
report  for  black  rot,  may  account  for  out-croppings  of  apple  blotch 
in  healthy  orchards  at  some  distance  from  disease  centers. 

Man  is  the  most  important  agent  of  dissemination.  Apple  blotch 
is  frequently  found  in  Illinois  on  young  apple  trees  in  shipments  from 
nurseries  in  the  blotch  infested  area  of  the  United  States.  Adams1 
has  noted  several  instances  of  its  presence  in  Pennsylvania  on  nursery 
stock  from  the  Middle  West. 

The  great  danger  of  infesting  the  nurseries  lies  in  the  nursery- 
man's use  of  infected  American-grown  apple-seedling  stock.  The 
great  bulk  of  the  apple  seedlings  come  from  the  region  between  Ross- 
ville  and  Perry  in  the  Kaw  valley  of  Kansas.  Apple  blotch  has  been 
prevalent  in  Kansas  since  1903.  Conclusions  have  been  reached  to 
the  effect  that  American-grown  apple  seedlings,  especially  those  grown 
in  localities  where  apple  blotch  is  prevalent,  are  an  important  means 
of  distributing  the  disease,  especially  when  the  practice  of  budding 
is  followed.  There  is  sufficient  evidence  that  the  disease  is  frequently 
present  on  seedlings  coming  into  the  eastern  states  from  sections  west 
of  the  Mississippi  river. 


530  BULLETIN   No.   256  [February, 

In  Illinois  only  a  relatively  small  percentage  of  the  seedlings  are 
budded;  the  majority  are  grafted.  In  both  cases,  however,  even  tho 
the  stock  is  healthy,  the  danger  of  making  diseased  trees  is  obvious 
since  80  to  90  percent  of  the  infection  appears  at  the  buds,  which 
sometimes  is  not  evident  until  the  spring  following  infection.  Since 
the  disease  is  so  prevalent  on  susceptible  varieties  in  the  east  and 
south-central  regions  of  the  United  States,  the  chances  of  selecting 
disease-free  buds  here  is  not  very  great  and  if  the  seedlings  are  grafted, 
the  probabilities  of  selecting  disease-free  scions  is  less.  There  is  no 
danger  of  disseminating  the  disease  on  seedling  stock  provided  it  is 
used  only  for  grafting  purposes,  topping  back  to  the  root  is  practiced, 
and  healthy  scions  are  employed. 


HISTORICAL  :     METHODS  THAT  HAVE  BEEN  ADVOCATED 

In  the  earliest  experiments  on  the  control  of  apple  blotch,  con- 
ducted by  Crandall,23  Scott  and  Quaintance,77  and  Scott  and  Rorer,78 
measures  were  recommended  which  at  that  time  gave  satisfactory 
control  of  the  disease.  Crandall23' 2*  found  that  apple  blotch  yielded 
quite  readily  to  applications  of  liquid  Bordeaux.  In  1907  Scott  and 
Quaintance77  reported  that  the  periods  of  infection  were  about  the 
same  for  blotch  as  for  bitter  rot  and  recommended  the  same  treatment 
for  both  diseases ;  namely,  four  applications  of  Bordeaux  at  intervals 
of  two  weeks,  beginning  six  weeks  after  petal  fall.  This  schedule 
was  modified  later  by  Scott  and  Rorer78  under  the  belief  that  the 
principal  infections  occurred  from  four  to  six  weeks  after  the  petals 
had  fallen.  Consequently,  they  recommended  four  applications  of 
Bordeaux,  beginning  three  to  four  weeks  after  petal  fall,  again  four 
weeks  later,  and  the  third  and  fourth  applications  at  intervals  of  three 
weeks  thereafter.  The  second  and  succeeding  applications  cor- 
responded with  the  treatment  for  bitter  rot,  so  that  one  course  of 
treatment  controlled  both  diseases.  Hewitt46-  47  recommended  prac- 
tically the  same  schedule  for  blotch  and  bitter  rot  in  Arkansas.  The 
idea  of  applying  a  spray  three  weeks  after  petal  fall  for  blotch  orig- 
inated with  Dickens  and  Headlee25  of  Kansas.  The  most  satisfactory 
results  were  obtained  with  three  applications  of  Bordeaux  applied  at 
petal  fall  and  again  at  three  and  ten  weeks  later.  Lewis,51  in  1913, 
confirmed  these  results  and  recommended  an  identical  spraying 
schedule. 

Many  of  the  earlier  investigations  on  apple  blotch  control  have 
been  concerned  with  the  study  of  tbe  relative  merits  of  Bordeaux  and 
lime  sulfur.  In  1913  Lewis51  reported  that  lime  sulfur  was  less 
effective  than  Bordeaux  for  blotch  control,  and  that  by  the  continued 


1925}  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  531 

use  of  Bordeaux  during  successive  seasons  the  disease  could  be  almost 
completely  eradicated  from  the  orchard.  These  results  coincided  with 
those  of  Scott75' 76  in  Virginia  in  1910.  The  results  of  Blair  et  al8 
like  those  of  Scott,  and  Lewis,  showed  a  greater  efficiency  from  the 
use  of  Bordeaux.  The  treatment  which  seemed  to  be  of  most  value, 
however,  when  russet  and  foliage  injury  are  considered,  involved  the 
use  of  lime  sulfur  for  the  early  applications  and  Bordeaux  for  the 
later  applications.  On  the  basis  of  their  results,  it  seemed  that  ap- 
plications at  intervals  of  ten  days  after  petal  fall,  two  to  three  weeks 
later,  and  ten  weeks  after  petal  fall  were  worthy  of  recommendation 
in  Illinois,  using  lime  sulfur  for  the  first  two  applications  and  Bor- 
deaux for  the  ten-weeks  spray.  In  1915  Gunderson42  recommended 
the  substitution  of  lime  sulfur  for  Bordeaux  for  the  early  applications 
in  order  to  avoid  injuries  to  the  fruit  and  foliage.  He  recommended 
applications  at  three  weeks  after  petal  fall  and  at  sufficient  frequency 
thereafter  until  July  1  to  keep  the  fruit  coated.  In  1916  Gunderson43 
considered  Bordeaux  superior  to  lime  sulfur  for  blotch  and  stated 
that  applications  at  intervals  of  three,  five,  and  seven  weeks  after 
petal  fall  were  the  important  sprays.  Walton104  offered  the  same 
recommendations  for  Ohio,  with  the  exception  that  where  the  disease 
is  light  or  there  is  danger  of  injury  from  Bordeaux,  lime  sulfur  should 
be  used.  The  results  of  the  spraying  experiments  of  Gunderson44  in 
1917  and  1918  showed  that  the  lime  sulfur  and  Bordeaux  sprays  were 
equally  effective  and  that  the  three-  and  five-weeks  sprays  were  the 
most  important. 

In  1918  Brock10  employed  a  schedule  consisting  of  applications 
three,  five,  seven,  and  nine  weeks  following  the  bloom,  and  reported 
inconclusive  and  disappointing  results,  stating  that  it  was  impossible 
to  bring  blotch  under  satisfactory  control  in  a  neglected,  susceptible 
orchard  in  one  or  two  years.  Brock  believed  that  very  susceptible 
varieties  should  receive  applications  of  lime  sulfur  or  Bordeaux  at 
intervals  of  three,  four,  five,  and  six  weeks  after  the  bloom.  He12 
considered  the  six-weeks  application  generally  unnecessary  and  con- 
sequently recommended  the  three-,  four-,  and  five-weeks  applications 
under  the  belief  that  no  infections  occur  later  than  five  weeks  after 
petal  fall. 

The  results  of  Gunderson45  for  the  three-year  period  1916  to  1918 
showed  that  applications  three  weeks  and  five  weeks  after  petal  fall, 
with  additional  sprays  under  conditions  of  heavy  rains,  successfully 
controlled  apple  blotch  and  that  the  results  from  Bordeaux  and  lime 
sulfur  were  practically  equal. 

In  Nebraska,  Cooper,20  working  on  the  assumption  that  the  primary 
and  greatest  infections  occur  during  the  four-  to  five-weeks  period  after 
petal  fall,  recommended  a  schedule  involving  applications  of  Bordeaux 


532  BULLETIN   No.   256  [February, 

three  weeks  after  petal  fall,  again  when  spraying  for  the  second- 
brood  codling  moth,  and  an  additional  intermediate  spray  five  weeks 
after  petal  fall  for  heavily  infected  orchards.  Cooper's  results  also 
claimed  the  superiority  of  Bordeaux  over  the  lime  sulfur. 

In  Oklahoma,55  on  the  basis  of  five  years'  work,  the  Experiment 
Station  reports  the  worthlessness  of  the  lime  sulfur  spray  for  apple 
blotch  control.  For  effective  control,  applications  of  Bordeaux  mix- 
ture are  recommended  at  intervals  of  2,  4,  5,  and  7  weeks  after  the 
petals  fall. 

Ballou  and  Lewis4  of  Ohio,  on  the  basis  of  one  season's  work,  ob- 
tained excellent  control  of  blotch  with  Bordeaux  sprays  following  a 
2,  4,  10  weeks  schedule.  The  same  schedule  with  lime  sulfur  was 
much  less  effective  but  produced  the  only  really  smooth,  bright,  and 
attractive  apples.  It  is  interesting  to  note,  however,  that  where  the 
2,  4,  6,  10  weeks  schedule  with  lime  sulfur  was  followed,  the  results 
were  as  good  as  with  the  Bordeaux  sprays. 

With  the  introduction  of  dusts  as  substitutes  for  sprays  attempts 
were  made  to  control  apple  blotch  with  dusts.  The  first  experiments 
by  Crandall23' 24  with  Bordeaux  dust  demonstrated  that  the  dust  was 
inefficient  in  controlling  the  dominant  apple  fungi  among  which 
P.  solitaria  was  included ;  a  conclusion  which  was  likewise  reached  by 
Fromme8  et  al34  from  two  years'  experiments  with  Bordeaux  dusts  in 
Virginia,  contrary  to  the  earlier  report  of  Fromme  and  Ralston33  that 
control  with  Bordeaux  dust  was  as  striking  as  it  was  unexpected.  In 
1918  Brock11  reported  the  failure  of  sulfur  dusts  to  control  apple 
blotch  in  Illinois,  and  Giddings,38  experimenting  with  various  types 
of  dusts,  stated  that  dusts  could  not  be  recommended  in  West  Vir- 
ginia for  the  control  of  apple  blotch  or  any  of  the  dominant  apple 
fungi. 

A  new  era  appeared  in  the  history  of  apple  blotch  control  when 
the  spraying  results  of  Rolfs72  in  Oklahoma,  Brock14  in  Illinois,  Stover 
et  al54>  90  and  Beach5'7  in  Ohio,  emphasized  the  need  of  applying  a 
spray  somewhat  earlier  than  the  three-weeks  application.  On  the 
basis  of  their  results,  the  two-weeks  spray  has  been  recommended  in 
many  states  as  the  first  spray  in  the  schedule  for  the  control  of  this 
disease.  In  Illinois,  Brock14  observed  that  better  control  was  possi- 
ble with  the  application  of  the  two-weeks  spray  of  either  lime  sulfur 
or  Bordeaux.  The  results  convinced  him  that  blotch  infections 
must  occur  in  many  seasons  prior  to  three  weeks  after  petal  fall. 
Beach's  results  from  the  two-,  four-,  six-,  and  ten- weeks  spray  schedule 
with  hydrated  lime-Bordeaux  demonstrated  the  possibility  of  obtain- 
ing perfect  control  of  apple  blotch  in  Ohio  under  the  most  severe 
cases  of  infection.  We  are  indebted  to  Rolfs,72  however,  for  first 


•Information  obtained  from  personal  correspondence. 


1925]  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  533 

emphasizing  the  necessity  of  an  application  at  two  weeks  after  petal 
fall.  He  states,  "The  spring  of  1918  was  unusually  wet  and  we 
failed  to  get  our  second  spray  on  the  trees  until  about  the  middle  of 
the  third  week.  Consequently  fully  50  percent  of  the  apples  became 
infected  with  the  blotch  organism  (Phyllosticta  solitarium).  The 
results  .  .  .  show  that  the  second  spray  if  applied  in  three  weeks  is 
not  soon  enough  to  prevent  the  early  blotch  infections  ..."  This 
has  also  only  recently  been  found  to  be  true  for  Pennsylvania 
conditions.89 

Supplementary  to  the  use  of  fungicides  for  the  control  of  apple 
blotch  many  investigators  have  stressed  pruning  of  the  cankered 
branches,  for  it  has  been  known  from  the  earliest  investigations  that 
the  cankers  serve  as  the  annual  sources  of  inocula.  Others  have 
recommended  a  general  thinning-out  pruning  before  the  spraying 
season  begins  in  order  to  facilitate  more  thoro  and  general  distribution 
of  the  sprays. 

Beach,5  in  1922,  suggested  fertilization  of  weak  and  badly  diseased 
trees  with  nitrate  of  soda  or  sulf  ate  of  ammonia  to  induce  an  abundance 
of  new  growth  which  could  be  kept  free  from  cankers  by  spraying 
and  which  would  gradually  build  up  a  healthy  fruit  spur  system. 

Dormant  Spraying 

As  early  as  1910  apple  growers  in  some  sections  of  southern  Illi- 
nois observed  that  dormant  applications  of  lime  sulfur  or  copper  sul- 
fate  were  of  some  value  in  reducing  the  amount  of  apple  blotch  on 
the  fruit.  No  experiments,  however,  had  been  undertaken  to  deter- 
mine this  point.  Watkins106' 107  as  early  as  1912  stated  from  field 
observations  that  the  difference  in  the  amount  of  infection  on  trees 
receiving  and  not  receiving  the  winter  lime-sulfur  application  was 
not  sufficient  to  attract  attention  and  yet,  without  the  confirmation 
of  any  experiments,  he  felt  that  winter  applications  of  lime  sulfur 
should  reduce  the  amount  of  infection  by  permitting  less  potential 
inocula.  Watkins  strongly  urged  upon  the  growers  the  necessity  of 
this  spray  primarily  for  scale,  but  his  great  confidence  in  it  as  a 
bark  spray,  and  his  desire  to  see  growers  acquire  the  practice  of 
dormant  spraying,  led  him  to  recommend  it  as  •  well  for  superficial 
bark  diseases  like  bitter  rot  and  blotch.  Wallace,103  experimenting  on 
this  phase  of  blotch  control  in  Indiana,  claimed  remarkable  results 
with  an  application  of  strong  lime  sulfur  and  stated,  ' '  It  seems  prob- 
able that  this  disease  which  costs  Indiana  growers  as  much  as  any 
other  apple  disease  will  eventually  be  controlled  by  winter  spraying. ' ' 
The  assumption  was  also  made  that  there  would  be  fewer  fungus 
spores  left  to  start  infections.  Later,  Douglass27-29  claimed  that  one 
dormant  application  of  a  very  strong  lime-sulfur  solution  "would 


534  BULLETIN   No.   256  [February, 

eat  its  way  into  the  shallow  canker  and  kill  the  fungus  in  its  strong- 
hold. ' '  Gunderson  's44>  45  results  show  that  dormant  applications  of 
copper  sulfate,  lime  sulfur,  or  Scalecide  have  no  effect  upon  the  growth 
of  the  cankers  or  upon  pycnidial  formation  and  "altho  no  examina- 
tions were  made  for  spores,  it  is  reasonable  to  conclude  that  these 
were  produced."  Brock,14  from  the  results  of  several  experiments, 
and  Oskamp58  have  also  reported  no  apparent  blotch  control  from 
dormant  sprays. 

The  failure  to  recognize  the  merits  of  certain  dormant  sprays  for 
blotch  control  has  resulted  from  the  fact  that  investigators  have 
measured  the  effect  of  these  sprays  entirely  by  the  amount  of  blotched 
fruit.  Their  effort  was  directed  primarily  to  the  extermination  of 
the  organism  from  the  living  tissues  by  external  applications  of  toxic 
substances,  not  realizing  the  close  association  between  fungus  and 
host,  and  the  existence  of  the  fungus  in  the  raised  margins  of  the 
cankers  securely  protected  from  the  influence  of  any  chemical.  None 
of  these  investigators  used  the  microscope  in  the  field  to  determine 
the  actual  condition  of  the  spores  after  the  applications. 

In  the  absence  of  such  microscopic  evidence  they  were  at  a  loss 
to  explain  their  negative  results.  The  fact  that  there  was  no  apparent 
difference  in  the  percentage  of  control  on  trees  receiving  only  the 
regular  summer  sprays  and  trees  receiving  the  dormant  spray  in 
addition  is  obvious.  Indeed,  in  some  seasons  during  these  years, 
growers  occasionally  observed  a  marked  difference  in  infection  on 
trees  receiving  and  not  receiving  the  dormant  spray,  and  their  results 
led  them  to  continue  the  practice  of  late  dormant  spraying.  The 
diversity  of  results  among  growers  and  investigators  was  due  to  the 
varied  conditions  of  spraying,  that  is,  the  kind  of  spray,  the  time 
and  frequency  of  the  applications,  the  thoroness  of  the  applications, 
and  the  amount  of  infection,  and  to  other  factors  inherent  in  the 
habit  of  the  cankers. 

The  Department  of  Botany  of  the  Purdue  Agricultural  Experi- 
ment Station63' 64  found  from  laboratory  tests  that  a  strong  lime- 
sulfur  solution  killed  the  spores  of  the  fungus  in  exposed  pycnidia 
and  not  the  mycelium  in  the  tissues  of  the  bark,  but  their  field  ' '  results 
of  1919  indicated  that  the  dormant  spray  does  not  in  any  way  diminish 
blotch  infection  on  the  fruit  and  foliage."  The  writer40'41  claimed 
that  for  reasons  connected  with  the  habit  and  life  history  of  the 
fungus  it  is  possible  to  destroy  a  percentage  of  the  season's  infections 
with  late,  strong  applications  of  copper  sulfate  or  lime  sulfur,  but  that 
the  extermination  of  the  fungus  by  spraying  is  impossible.  This  report 
also  stated  that  the  summer  sprays  were  absolutely  necessary  to  con- 
trol the  disease.  In  confirmation  of  this  report,  Brock16  recently  has 
stated,  "Heavy  applications  of  lime  sulfur  at  winter  strength  applied 
at  the  delayed  dormant  stage  are  partially  effective  in  reducing  the 


1985]  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  535 

percentage  of  infection,  altho  their  use  alone  would  not  be  considered 
as  approaching  control." 

EXPERIMENTS  WITH  DORMANT  SPRAYS 

As  has  been  mentioned  previously,  the  cankers  remain  relatively 
dormant  during  the  winter  months,  altho  their  increase  in  size  and 
the  formation  of  pycnosclerotia  occur  during  this  period  under  warm, 
moist  conditions.  In  the  spring  after  the  buds  swell  and  open,  a  rapid 
enlargement  of  the  canker  is  effected  and  true  pycnidia  are  formed 
whose  spores  play  an  important  part  in  the  season 's  infections. 

Previously  it  has  been  stated  that  differentiation  of  the  pycno- 
sclerotia begins  in  March  and  that  distinct  spores  are  present  in 
March  and  April.  The  pycnosclerotia  may  become  exposed  at  the  time 
of  their  formation  in  autumn,  in  winter,  or  in  the  following  spring. 
Obviously  the  nearer  the  development  of  the  pycnosclerotia  approaches 
the  period  of  blossoming  and  initial  infection,  the  greater  is  the  number 

TABLE  15. — APPROXIMATE  NUMBER  OF  EXPOSED  AND  UNEXPOSED  PYCNOSCLEROTIA 

ON  CANKERS  EXAMINED  AT  INTERVALS  DURING  SPRING 

OF  1923  AT  URBANA 


Number  of  cankers 
examined 

Date  of 
examination 

Number  of 
pycnosclerotia 

Number 
exposed 

Number 
unexposed 

Percentage 
exposed 

21 
26 

February  7  .  . 
March  23  

1039 
1017 

245 
491 

794 
526 

23.6 
48.3 

of  exposed  pycnosclerotia.  In  other  words,  before  the  dormant  season 
for  the  host  terminates  some  of  the  pycnosclerotia  are  covered,  some 
exposed,  and  no  matter  how  late  the  strong  dormant  spray  is  applied 
not  every  pycnosclerotium  can  be  touched.  It  is  common  to  find 
pycnosclerotia  on  the  outer,  purplish  areas  of  the  older  cankers  cov- 
ered even  late  in  the  dormant'  season,  because  the  thickness  and 
strength  of  the  bark  prevents  their  exposure.  One-year  wood  and, 
particularly,  water  sprouts  show  many  exposed  pycnosclerotia  be- 
fore the  winter  begins.  Table  15  shows  the  relative  number  of  exposed 
and  covered  pycnosclerotia  on  cankers  in  February  and  March,  1923. 
In  order,  therefore,  to  get  the  greatest  advantage  from  dormant 
sprays  for  blotch  control,  it  is  necessary  to  delay  the  application  as 
late  as  the  trees  will  tolerate  it  without  injury.  Growers  frequently 
apply  the  dormant  spray  when  the  buds  are  beginning  to  show  pink 
color.  This  late  application  would  be  very  desirable  since  most  of  the 
pycnosclerotia  are  then  exposed,  were  it  not  for  the  fact  that  the  trees 
cannot  then  be  drenched  without  causing  some  injury.  Therefore,  the 
application  should  be  made  a  little  earlier  when  the  buds  are  swelling 
and  are  green,  even  tho  not  as  many  prospective  infections  are  likely 
thus  to  be  suppressed. 


536 


BULLETIN   No.   256 


[February, 


TABLE  16. — DIFFERENCE  IN  THE  NUMBER  OF  APPLE  BLOTCH  INFECTIONS  ON 

DUCHESS  APPLES  AS  THE  RESULT  OF  DORMANT  SPRAYS 

AT  ANNA,  JUNE,  1920 


Dormant  treatment 

Number  of  apples 
examined 

Total  number  of 
infections 

Scalecide  

15 

327 

Lime  sulfur  (1-8)  

15 

217 

Hcaleoide  

15 

257 

Lime  sulfur  (1-4)  

15 

120 

Scalecide  

15 

275 

Lime  sulfur  (1-8)  

15 

213 

Another  factor  which  deserves  emphasis  is  the  need  of  thoroness 
in  the  applications.  Every  exposed  pycnosclerotium  must  be  covered 
by  the  fungicide  if  it  is  hoped  to  kill  the  spores  within.  Slipshod 

methods  of  spraying,  appli- 
cations from  one  side  of  the 
trees,  and  incomplete  cover- 
ing of  the  trees  have  been  in 
part  responsible  for  the  con- 
tradictory results.  Every  por- 
tion of  the  bark  must  be  cov- 
ered. 

The  nature  and  strength 
of  the  spray  is  of  fundamen- 
tal importance.  Late  in 
March,  1920,  at  Anna,  Duch- 
ess and  Benoni  trees  were 
sprayed  with  commercial  lime 
sulfur  (32°  Baume,  l-4y2) 
and  others  with  copper  sul- 
fate  ( 1-41/2).  Both  sprays 
effective  in  killing  the 

NOSCLEROTIA    FROM    CANKERS    SPRAYED  .    ,  . 

WITH  COMMERCIAL  LIME  SULFUR  32°         spores.     In  a  neighboring  or- 
BAUME,  1-8,  LATE  DORMANT  SEASON  chard     Duchess     trees     were 

sprayed  with  commercial  lime 

sulfur  (32°  Baume,  1-8)  on  March  29  and  30  with  the  same  results. 
Scalecide  applied  at  the  same  time  and  at  the  rate  of  4  gallons  of 
Scalecide  to  50  gallons  of  water  had  no  apparent  effect  upon  the 
spores.  In  tallying  the  amount  of  infection  on  the  trees  receiving 
and  not  receiving  the  effective  dormant  sprays  no  difference  was 
apparent  in  the  amount  of  infected  fruit,  altho  counts  of  the  num- 
ber of  infections  on  apples  from  trees  sprayed  with  Scalecide  and 
from  trees  sprayed  with  lime  sulfur,  showed  that  there  was  a  differ- 
ence in  the  number  of  infections,  and  that  the  difference  was  greater 
on  the  apples  from  trees  which  received  the  double  strength  of  lime 
sulfur,  as  is  shown  in  Table  16. 


19  S5} 


APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL 


537 


Since  Scalecide  had  no  toxic  effect  on  the  spores  the  trees  receiving 
only  this  spray  may  be  regarded  as  unsprayed  so  far  as  blotch  infec- 
tion is  concerned.  The  apples  from  which  the  data  in  Table  16  were 
obtained  were  picked  at  random  from  the  trees  and  the  picking  was 
done  blindfolded.  The  percentage  and  number  of  seriously  and 
slightly  infected  apples  from  these  pickings  are  found  in  Table  17. 

TABLE  17. — NUMBER  AND  PERCENTAGE  OF  INFECTED  DUCHESS  APPLES  FROM  TREES 
SPRAYED  WITH  SCALECIDE  AND  WITH  LIME  SULFUR 


Dormant  treatment 

Number  of  apples 
examined 

Apples  seriously  infected 

Apples  slightly  infected 

Number 

Percentage 

Number 

Percentage 

Scalecide  

45 
45 

37 
29 

82 
64 

8 
16 

18 
36 

Lime  snlfur  

In  these  tables  "slightly  infected"  is  interpreted  to  mean  less  than 
six  infections  per  apple,  "seriously  infected,"  more  than  five  infec- 
tions. Commonly,  the  seriously  infected  fruit  bore  as  many  as  fifty 
or  more  infections.  Of  forty-five  apples  examined  from  the  trees 
receiving  Scalecide,  twenty  apples  showed  more  than  twenty  infec- 
tions, eight  of  which  showed  more  than  forty  infections;  while  of 

TABLE  18. — EFFECT  OF  DORMANT  SPRAY  UPON  AMOUNT  OF  APPLE  BLOTCH  ON 
DUCHESS  APPLES  (after  W.  S.  Brock") 

Percentage  affected 


Serious 

Slight 

Total 

Free 

Double  strength  lime  sulfur  

35.2 

48.5 

83.7 

16.3 

No  dormant  

76.7 

2.2 

78.9 

21.1 

forty-five  apples  examined  from  the  trees  receiving  lime  sulfur,  twelve 
showed  more  than  twenty  blotches  of  which  only  three  showed  more 
than  forty  blotches.  Brock16  recently  has  reported  some  control  of 
apple  blotch  with  dormant  lime  sulfur  (Table  18).  The  real  differ- 
ences in  the  number  of  infections  appear  in  the  percentage  of  slightly 
and  seriously  infected  fruit. 

On  March  22,  1921,  at  Anna,  three  Benoni  trees  were  given  a  heavy 
application  of  homemade  lime  sulfur  (31°  Baume,  1-S1/^).  At  the 
time  of  the  application,  the  fruit  buds  were  showing  pink  color  and 
the  young  leaves  were  well  exposed.  The  spraying  was  done  under 
windy  conditions  and  altho  drenching  was  resorted  to,  microscopic 
examination  of  the  spores  on  March  31,  and  later  in  the  season,  showed 
that  generally  they  were  not  killed,  even  in  cankers  which  were 
specifically  marked  and  heavily  covered  with  the  spray.  This  led  the 
writer  to  lose  confidence  in  homemade  lime  sulfur  for  dormant  spray- 
ing of  apple  blotch  control.  In  another  portion  of  the  same  orchard, 
Duchess,  Ben  Davis,  and  Rome  Beauty  trees  were  sprayed  late  with 
the  lime  sulfur  (com.  33°  Baume,  1-8)  and  examinations  of  the 


538 


BULLETIN   No.   256 


[February, 


pycnidia  from  these  trees  on  April  10,  1921,  revealed  the  dead  col- 
lapsed condition  of  the  spores,  altho  several  pycnidia  were  found  full 
of  apparently  normal  spores.  Other  blocks  of  Duchess  trees  in  the 
orchard  were  sprayed  in  December,  and  again  in  March  with  lime 
sulfur  (com.  32°  Baume,  1-8)  and  no  pycnidia  could  be  found  with 
normal  spores  on  March  22,  1921.  However,  since  the  fungus  was 
not  killed,  the  cankers  enlarged  in  April  and  a  new  source  of  in- 
fection arose.  Nevertheless,  the  fruit  on  these  trees  was  relatively 

TABLE  19. — EESULTS  FROM  TREATMENT  OF  CANKERS  WITH  CHEMICALS  LATE  IN  THE 
DORMANT  SEASON,  URBANA,  1922 


Treatment 

First  application 

Second  application 

Resultt 

Strength 

Date 

Strength 

Date 

\\i-50 
4-50 
6-50 
20-50 
1-5 

April  3  

1  qt.-15  gals. 
3^-50         ,  < 
3^-50 
13-50 
(Not  duplicated) 

April  15.  .  . 

+ 

Aoril  3  

April  13  

Spra-Mulsion  

April  3  

April  13  

April  3 

April  13   ... 

Copper  sulfate  

April  13  

1  (  — )  indicates  that  the  spores  were  not  affected;  (+)  indicates  that  the  spores  were  affected. 

free  of  blotch  when  the  orchard  was  examined  on  May  27,  while 
in  a  neighboring  Duchess  orchard  where  the  dormant  spraying 
was  only  partially  effective  in  killing  the  spores,  and  where  the  trees 
were  much  less  severely  cankered,  the  apples  were  quite  heavily  in- 
fected. Similar  results  have  often  been  observed  by  growers. 

In  the  spring  of  1922,  dormant  spraying  experiments  were  under- 
taken on  Northwestern  Greening  trees  in  the  University  Orchards 
at  Urbana.  The  materials  used  were  Phenolene,  Sealecide,  Spra- 
Mulsion,  copper  sulfate,  and  dry  lime  sulfur.  Two  dormant  appli- 
cations were  made  with  each  solution  excepting  with  copper  sulfate, 
as  noted  in  Table  19.* 

On  April  23  and  June  5,  cankers  from  the  trees  receiving  these 
applications  were  brought  into  the  laboratory  and  it  was  found  that 
the  pycnidia  and  spores  from  the  trees  receiving  the  strong  copper- 
sulfate  spray  were  dead.  All  other  sprays  applied  had  no  effect  upon 
the  fungus.  No  data  were  taken  upon  the  relation  of  these  dormant 
sprays  to  the  amount  of  infection  upon  the  fruit,  since  the  trees  were 
adjacent  to  one  another  in  the  same  row.  In  a  near-by  orchard  a 
heavily  cankered  tree  was  sprayed  on  April  3  with  copper  sulfate  in 
the  proportion  of  1  pound  of  copper  sulfate  to  15  gallons  of  water 
and  the  examination  of  the  pycnidia  later  in  the  season  showed  the 
toxic  effect  of  the  fungicide. 

The  evidence  obtained  from  these  experiments  with  dormant  sprays 
indicates  that  it  is  possible  to  reduce  the  amount  of  the  season 's  inf ec- 


"The  Phenolene,  Spra-Mulsion,  and  dry  lime  sulfur  were  furnished  by  the 
Sherwin-Williams  Company;  the  Sealecide  by  the  Pratt  Fungicide  and  Insecti- 
cide Company. 


19S5]  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  539 

tion  by  dormant  spraying  with  commercial  lime  sulfur  or  copper 
sult'ate.  It  seems  from  these  results  that  a  dilution  of  commercial 
lime  sulfur  (32°  Baume,  1-8)  recommended  for  San  Jose  scale  in 
Illinois  orchards  is  strong  enough  to  kill  the  spores  in  the  exposed 
pycnidia.  The  experiments  also  show  that  copper  sulfate  (l-4!/2  and 
1-15)  produces  the  same  effect.  Until  more  definite  evidence  is  secured 
a  solution  of  copper  sulfate  prepared  in  the  proportion  1-10  can  be 
applied  with  the  assurance  of  success,  since  the  greater  the  concentra- 
tion, the  greater  the  deposit,  and  the  less  rapidly  the  material  is  likely 
to  wash  from  the  branches  or  become  too  diluted  before  accomplishing 
its  effect.  The  practice  of  applying  two  dormant  sprays  for  bark- 
susceptible  varieties  of  apples  has  been  followed  by  some  southern 
Illinois  orchardists  and  is  a  sound  one.  For  the  purpose  of  suppressing 
as  much  prospective  infection  as  possible,  it  is  particularly  desirable 
to  spray  as  late  as  possible.  The  spring  applications  are  also  more 
effective  than  the  autumn  applications  for  the  control  of  San  Jose 
scale.  It  is  suggested  that  the  entire  orchard  be  sprayed  with  com- 
mercial lime  sulfur  (32°  or  33°  Baume,  1-8)  primarily  for  scale,  and 
the  blotch-cankered  varieties  again  very  late  with  copper  sulfate  (1- 
10).  With  the  present  cheap  price  of  copper  sulfate  and  the  value 
that  can  be  derived  from  this  spray,  southern  Illinois  growers  can 
well  afford  its  application.  If  the  duplicate  application  is  not  pos- 
sible, then  the  application  of  commercial  lime  sulfur  only  (32°  or 
33°  Baume,  1-8)  for  the  bark-susceptible  varieties  should  be  post- 
poned as  late  as  the  trees  will  tolerate  it. 

The  writer  claims  that  the  dormant  spray  reduces  the  season's 
infections,  but  since  the  remaining  infection  that  does  not  come  within 
the  reach  of  the  dormant  spray  may  be  large,  the  difference  between 
the  amount  of  disease  on  the  fruit  of  those  trees  receiving  and  those 
not  receiving  the  application  may  not  be  sufficient  to  attract  attention. 

Effect  of  the  Fungicide 

The  difference  in  the  appearance  of  the  spores  affected  by  chemicals 
and  the  normal  spores  is  very  striking.  In  contrast  to  the  normal 
turgid,  broadly  elliptical  spores  containing  large  globules  (Fig.  9 A), 
the  affected  spores  are  collapsed,  like  irregularly  shaped  rods  or  clubs, 
usually  retaining  the  attached  collapsed  appendage  (Fig.  J6).  The 
original  globules  in  the  spore  cell  are  united  into  an  irregular,  homo- 
geneous mass  and  their  individuality  lost.  The  pycnidia  affected  by 
the  fungicide  are  brittle,  rigid,  and  inflexible,  and  the  dead  spores 
can  be  pressed  from  them  only  with  difficulty.  In  the  summer,  the 
contents  of  these  pycnidia  are  dry  and  collapsed  into  a  hard  mass 
and  the  individual  spores  lose  their  identity  (Figs.  17,  18). 


540 


BULLETIN   No.   256 


[February, 


The  pycnidia  are  conspicuously  larger  after  rains  than  during  dry 
periods,  due  to  the  swelling  of  the  concentrated  food  materials  in  the 
gelatinous  matrix.  When  cankers  are  covered  with  lime  sulfur  or 
copper  sulfate  it  is  evident  that  these  chemicals  in  solution  over  the 


FIG.  17. — SECTIONS  THRU  PYCNOSCLEROTIA,  SHOWING  THE  EFFECT 
OF  DORMANT  SPRAY 

(A)  Collected  June  7,  1920,  from  canker  sprayed  with  copper 
sulfate;  (B)  higher  magnification  of  A,  showing  the  dead, 
irregular  content  of  the  pycnosclerotium. 

cankers  are  carried  into  the  matrix  of  the  exposed  pycnosclerotia. 
Therefore,  during  wet  periods,  the  effect  of  these  substances  may  be 
expected  to  be  at  the  maximum.  Cooper21  found  that  the  stromata  of 
Nummularia  discreta  absorbed  copper  sulfate  and  lime  sulfur  readily 


1925] 


APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL 


541 


in  solution,  with  the  result  that  the  quantities  of  spores  expelled  and 
the  percentage  of  germinations  were  considerably  reduced.  The 
greatest  effect  was  obtained  with  copper  sulfate.  He  suggested  spray- 
ing the  cankers  with  copper  sulfate  at  the  rate  of  1  pound  to  2  gallons 
of  water  as  one  means  of  preventing  the  dissemination  of  ascospores 
in  the  spring.  For  use  on  apple  blotch  cankers  the  copper  sulfate 
seems  to  be  more  desirable  than  lime  sulfur.  The  fact  that  it  is 


FIG.  18. — SECTIONS  THRU  PYCNOSCLEROTIA 

(A)  From  canker  receiving  dormant  spray,  collected  April  18,  1920;  (B)  from 
an  unsprayed  canker,  collected  March  21,  1920. 

readily  soluble,  and  that  the  solution  readily  passes  into  the  fungus 
and  the  dead  tissues  of  the  canker,  and  that  it  persists  in  these  por- 
tions long  after  the  application,  gives  it  an  added  advantage. 

To  illustrate  the  need  of  moisture  to  produce  the  maximum  effect 
with  the  fungicides,  the  following  observations  are  noteworthy.  On 
March  30,  1920,  at  Anna,  Duchess  trees  were  sprayed  with  commer- 
cial lime  sulfur  (32°  Baume,  l-4i^>).  On  the  night  of  March  31  there 
was  a  heavy  rain  and  the  following  morning  pycnidia  from  these  trees 
were  examined  and  the  contents  found  to  be  dead.  Four  young 
Duchess  trees  in  another  orchard  at  Anna  were  drenched  with  copper 
sulfate  (l-4Vk)  and  on  the  following  day  most  of  the  spores  appeared 
normal,  no  precipitation  occurring  between  the  time  of  application 
and  the  observation.  A  few  days  later  a  heavy  rain  fell  and  when  the 
spores  were  examined  on  April  8  after  the  rain  they  were  dead 
(Plate  4).  It  seems  then,  that  the  spray  alone  is  not  sufficient  to  carry 
the  chemicals  into  the  pycnidium  and  that  a  wetting  is  necessary  to 
soak  and  soften  the  carbonaceous  membrane. 

EXPERIMENTS  WITH  SUMMER  SPRAYS  .. 

The  plan  of  the  spraying  experiments  has  been  based  largely  on 
the  life  history  of  the  fungus.  The  results  of  the  treatments  con- 


542 


BULLETIN   No.   256 


[February, 


TABLE  20. — PLAN  OF  APPLE  BLOTCH  CONTROL  EXPERIMENT,  ANDERSON  DUCHESS 

ORCHARD,  ANNA,  1920 


Plat 
No. 

Treatment 

Applications 

Calyx 

2  wks. 

3  wks. 

4  wks. 

5  wks. 

6  wks. 

7  wks. 

1 

2 
3 
4 

5 
6 

7 
8 
9 
10 
11 
12 

13 
14 

15 
16 

17 
18 

19 

X 

X 

X 

X 

X 

X 

X 
X 

X 

X 

X 

X 

X 

X 

Check  

X 

X 

X 

X 

.. 

Lime  sulfur  

X 
X 

X 

X 
X 

X 

X 

X 

X 
X 

X 

Lime  sulfur  

X 

X 

X 

X 

X 

X 

Lime  sulfur  

X 

X 

X 

X 

X 

X 

Lime  sulfur  

X 

X 

X 

X 

X 

X 

Lime  sulfur  

X 

Bordeaux  

X 

X 

X 

X 

X 

Lime  sulfur  

X 

Bordeaux  

X 

X 

X 

X 

X 

.. 

Lime  sulfur  

X 

Bordeaux  

X 

X 

X 

X 

X 

X 

Lime  sulfur  

X 

Bordeaux  

X 

X 

X 

X 

X 

X 

X 

X 
X 

X 
X 

Bordeaux  

X 

X 

X 

X 

X 

Bordeaux  

Lime  sulfur  

X 

X 

Bordeaux  

Lime  sulfur  

X 
X 

X 
X 

X 
X 

X 
X 

X 

Lime  sulfur  

Bordeaux  

Lime  sulfur  

X 

X 

X 

X 

Bordeaux  

Lime  sulfur.  .  . 

X 

X 

X 

NOTE. — All  Bordeaux  was  of  the  3-4-50  formula.  All  lime  sulfur  was  of  the 
1-50  formula,  commercial  32°  Baume.  All  sprays  combined  with  powdered  arsenate 
of  lead  1-50. 

ducted  by  growers  under  the  supervision  of  the  writer,  and  the  re- 
sults of  the  experiments  of  the  writer  are  based  on  field  work  of  three 
seasons  at  several  localities  in  Illinois.  The  control  work  has  been 
largely  of  a  demonstrative  nature  and  on  a  small  scale,  and  while 
extensive  data  have  not  been  obtained,  the  results  are  sufficiently  con- 
clusive to  warrant  the  statement  that  successful  control  of  the  disease 
with  sprays  is  possible  in  even  the  most  seriously  infested  orchards. 


PLATE  4. — SECTIONS  THRU  PYCNOSCLEROTIA 

(A,  C)  From  cankers  sprayed  late  in  the  dormant  season  with  copper  sulfate; 
(B,  D)  from  cankers  not  sprayed  in  dormant  season,  Anna,  May,  1920. 


1925]  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  543 

In  1920  at  Anna 

The  spraying  experiments  for  the  control  of  apple  blotch  were 
conducted  in  a  block  of  Duchess  trees  in  the  Anderson  orchard.  The 
trees  were  about  fifteen  years  old,  in  good  vigor,  and  they  seemed 
not  to  be  weakened  from  apple  blotch  altho  cankers  were  sufficiently 
abundant  to  cause  severe  injury  to  the  entire  apple  crop  in  the  ab- 
sence of  sprays.  In  June,  it  was  found  that  on  unsprayed  trees  sixty 
apples  picked  at  random  showed  on  each  apple  an  average  of  eighteen 
blotches. 

The  orchard  was  divided  into  plats  of  four  trees  each.  Various 
schedules  with  applications  of  Bordeaux  3-4-50  and  lime  sulfur  1-50 
with  arsenate  of  lead  were  employed  (Table  20).  The  schedules  called 
for  applications  at  two,  three,  four,  five,  six,  seven,  and  eight  weeks 
after  the  fall  of  the  petals.  Certain  applications  were  omitted  in 
some  plats,  since  the  purpose  of  the  experiment  was  to  determine 
which  schedule  and  treatment  would  give  most  satisfactory  control. 
A  sufficient  number  of  unsprayed  trees  was  left  for  adequate  compari- 
son. The  spraying  was  done  with  a  power  sprayer  and  bamboo  rods 
were  used  for  all  of  the  summer  sprays. 

The  dormant  spray  of  lime  sulfur  was  applied  when  the  buds  were 
opening  and  showing  green  (March  28  and  29),  the  cluster-bud  spray 
of  lime  sulfur  (1-40)  was  applied  on  April  17  and  18,  and  the  calyx 
spray  of  lime  sulfur  and  lead  arsenate  on  April  26  and  27  when  the 
petals  were  75  percent  fallen.  The  spray  two  weeks  after  petal  fall 
(commonly  called  the  first  blotch  spray),  was  delayed  until  seventeen 
to  nineteen  days  after  the  fall  of  the  petals  (May  14  and  15).  No 
difficulty  was  encountered  in  the  application  of  the  remaining  sprays. 

The  fruit  was  harvested  July  5  and  since  poor  control  was  obtained 
in  all  of  the  plats,  no  attempt  is  here  made  to  present  the  results  of 
the  treatments,  altho  the  study  of  the  results  afforded  a  means  of  ex- 
plaining the  failures  and  gave  evidence  regarding  the  time  and  con- 
ditions associated  with  infection.  The  failure  to  apply  the  first  blotch 
spray  on  time — two  weeks  after  petal  fall  and  prior  to  the  rainy  period 
of  May  11  to  13 — and  the  fact  that  rains  were  continuous  during  the 
period  May  11  to  21,  favored  extensive  infection  of  the  fruit  and 
foliage.  Even  from  plats  receiving  all  of  the  other  sprays  in  the 
schedule  the  percentage  of  blotched  fruit  was  almost  equal  to  that 
from  unsprayed  trees  altho  the  number  of  infections  on  the  fruit  was 
considerably  less.  The  results  emphasized  the  fact  that  the  most  ex- 
tensive infections  of  the  season  may  occur  prior  to  the  three-weeks 
application.  The  serious  injury  to  the  fruit  from  early  applications 
of  Bordeaux,  i.e.,  at  petal  fall  and  two  weeks  after  petal  fall,  and  the 
absence  of  injury  from  treatments  of  lime  surfur  at  these  intervals, 
demonstrated  that  lime  sulfur  is  the  more  desirable  spray  for  early 
applications. 


544  BULLETIN    No.    256  [February, 

In  1921  at  Anna 

In  1921,  spraying  for  apple  blotch  control  was  conducted  in  a 
block  of  Benoni  trees  thirty-five  years  of  age  in  the  Miller  orchard. 
The  trees  were  badly  cankered  and  the  fruit  had  been  blotched 
severely  in  previous  years  in  the  absence  of  sprays.  The  age  of  the 
trees  necessitated  renovation,  which  consisted  in  the  removal  of  many 
of  the  top  branches,  dead  wood,  and  crowding  branches ;  a  more  uni- 
form distribution  of  the  sprays  thus  being  possible.  Unfortunately 
late  frosts  killed  most  of  the  blossoms;  however,  a  sufficient  amount 
of  fruit  set  to  warrant  the  continuation  of  the  experiment. 

Bordeaux,  hydrated  lime-Bordeaux  mixture,  and  homemade  lime 
sulfur  testing  31°  Baume  were  used  as  sprays,  and  all  of  the  applica- 
tions were  combined  with  powdered  arsenate  of  lead  in  the  proportion 
of  1  pound  to  50  gallons  of  water.  The  spraying  was  done  with  a 
power  sprayer  at  a  pressure  of  250  pounds  and  rods  were  used  ex- 
clusively. 

The  dormant  spray  was  applied  to  all  of  the  plats  on  March  20 
when  the  fruit  buds  were  beginning  to  show  pink.  It  served  the  pur- 
pose of  both  the  dormant  and  cluster  bud  sprays.  The  treatment  was 
homemade  lime  sulfur  testing  31°  Baume  used  in  the  proportion  of 
1  gallon  of  lime  sulfur  to  7  gallons  of  water.  The  calyx  spray  was 
applied  on  April  9,  three  days  after  the  recorded  date  of  petal  fall 
(April  6)  with  the  same  fungicide  in  the  proportion  of  1-35  and  with 
the  addition  of  powdered  arsenate  of  lead  (1-50).  The  season  was 
abnormal  and  the  fall  of  the  petals  occurred  unusually  early. 

The  treatments  were  made  at  intervals  of  two,  three,  four,  five,  six, 
and  seven  weeks  after  petal  fall.  Various  omissions,  and  alternations 
between  lime  sulfur  and  Bordeaux,  were  made  in  the  spray  schedule 
(Table  21).  It  was  intended  originally  to  omit  the  two-weeks  spray 
in  Plats  2,  6,  12,  and  15,  but  because  of  the  high  wind  prevailing 
two  weeks  after  the  fall  of  the  petals  it  was  impossible  to  spray  the 
rest  of  the  orchard  without  spraying  the  trees  in  these  plats,  especially 
on  the  leeward  side  of  the  trees.  The  remaining  summer  sprays 
were  applied  under  ideal  weather  conditions.  Six  trees  were  main- 
tained as  checks,  three  of  which,  isolated  from  the  orchard  by  a  peach 
orchard,  had  been  treated  earlier  in  the  season  with  homemade  lime 
sulfur  (31°  Baume,  1-31/2).  As  previously  stated,  this -spray  had 
relatively  no  effect  upon  the  spores,  because  of  the  weakness  of  the 
fungicide  and  its  poor  application  under  conditions  of  strong  wind. 
Consequently,  these  three  trees  have  been  considered  in  the  same  class 
with  the  trees  in  Plat  15,  which  were  not  sprayed  at  all. 

Because  of  the  late  frosts,  the  fruit  was  thinned  out  severely  and 
the  result  of  this,  combined  with  heavy  pruning,  had  the  effect  of 


1925} 


APPLE  BLOTCH  :    ITS  ETIOLOGY  AND  CONTROL 


TABLE  21. — PLAN  OF  APPLE  BLOTCH  CONTROL  EXPERIMENT, 
MILLER  ORCHARD,  ANNA,  1921 


Plat 
No. 

Treatment 

Applications  and  dates 

2wks. 
Apr.  21 

3wks. 
Apr.  27-28 

4  wks. 
May  3-4 

5  wks. 
May  12 

6  wks. 
May  18 

7  wks. 
May  29 

1 

2 
3 

4 
5 

6 

7 

8 
9 

10 
11 

12 

13 
14 

15 

Hydrated  lime  bordeaux.  .  .  . 
Lime  sulfur  

X 

X 
X 

X 
X 

X 
X 

X 
X 

X 

X 

X 

X 

X 

X 
X 

X 

X 
X 

X 
X 

X 
X 
X 

X 
X 

X 
X 

X 
X 

X 
X 
X 

X 
X 
X 
X 

X 
X 

X 

X 
X 

X 

X 
X 

Hydrated  lime  bordenux.  .  .  . 

Hydrated  lime  bordeaux.  .  .  . 
Lime  sulfur  

Hydrated  lime  bordeaux.  .  .  . 

Bordeaux  

Lime  sulfur 

X 

Bordeaux  

Bordeaux  

Lime  sulfur  

X 

Bordeaux  

Lime  sulfur  

X 

Bordeaux  

Lime  sulfur  

X 
X 

Lime  sulfur  

Bordeaux  

Lime  sulfur  

X 

Bordeaux  

Lime  sulfur  

Lime  sulfur  

X 
X 

Lime  sulfur  

Check.  .  . 

NOTE. — All  hydrated  lime  Bordeaux  was  of  the  3-5-50  formula.  All  Bordeaux 
was  of  the  3-4-50  formula.  All  lime  sulfur  was  of  the  1-36  formula  (homemade 
31°  Baume).  All  sprays  combined  with  powdered  arsenate  of  lead  1-50. 

producing  large  apples.  Approximately  eighty  bushels  of  apples  were 
harvested  from  the  forty-seven  trees  in  the  orchard,  altho  some  trees 
bore  no  fruit.  The  apples  from  the  sprayed  trees  were  free  of  dis- 
ease and  spray  injury,  and  the  control  of  apple  blotch  was  perfect. 
The  fruit  from  the  check  trees  and  the  drops  from  these  trees  were 
gathered  and  sorted  into  three  classes,  namely,  blotch  free,  slightly 
blotched,  and  seriously  blotched  (Table  22). 

The  records  of  natural  infection  for  the  season  of  1921  at  Anna 
show  that  a  light  primary  infection  occurred  as  early  as  April  26 
and  27,  or  nineteen  to  twenty-one  days  after  petal  fall,  but  since  all 
of  the  trees  in  the  orchard  received  spray  two  weeks  after  petal 
fall  (April  21)  infection  was  prevented.  The  next — the  first  heavy 
infections — occurred  in  the  period  May  9  to  11.  Prior  to  this  many 
of  the  plats  had  already  received  three  blotch  sprays,  namely  two 
weeks  (April  21),  three  weeks  (April  27  and  28),  and  four  weeks 


546 


BULLETIN   No.   256 


[February, 


(May  3  and  4)  after  petal  fall,  and  since  every  plat  received  the  two- 
weeks  spray  and  either  the  three-or  four-weeks  spray  as  the  plan  of 
the  experiment  shows,  (Table  21),  no  infections  resulted. 


TABLE  22. — RESULTS  OF  THE  SPRAYING  EXPERIMENT  FOR  THE  CONTROL  OF  APPLE 

BLOTCH,  ANNA,  1921 


Number  apples 
examined 

Number  blotch- 
free 

Number  blotched 

Slightly 

Severely 

Total 

Percentage 

Unsprayed.  .  .  . 
Sprayed 

1,379 

186 
Perfect  control  in  all 
plats  

446 
0 

747 
0 

1,193 
0 

86.5 
0 

In  1922  at  Urbana 

The  Urbana  orchard  consisted  of  several  winter  varieties  of  apples, 
some  trees  of  which  were  severely  cankered  with  apple  blotch  and 
black  rot.  The  trees  were  about  thirty  years  old,  high,  and  bore  a 
considerable  amount  of  dead  wood.  In  order  to  improve  the  trees 
for  spraying  a  heavy  pruning  was  resorted  to  in  the  dormant  season. 
The  setting  of  fruit  in  1922  was  small  and  altho  some  trees  bore 
heavily,  the  amount  of  fruit  on  others  was  insignificant,  and  too  small 
for  the  purposes  of  the  experiment. 

The  spraying  was  done  with  a  power  sprayer  and  both  guns  and 
rods  were  employed.  The  dormant  spray  of  commercial  lime  sulfur 
(33°  Baume,  1-8)  was  applied;  late  in  the  dormant  season,  on  April  3 


TABLE  23. — TREATMENTS  AND  TIME  OF  APPLICATION  OF  SPRAYS  IN  THE  WEBBER 

ORCHARD,  URBANA,  1922 


Application 

Treatment 

Time  of  application 

Cluster  bud  

April  12 

Calyx  

Lime  sulfur  (1—50)  lead  arsenate  (1—50)   

May  2    (Petals  fallen  75%) 

Two  weeks  

Lime  sulfur  (1—50)  lead  arsenate  (1—50)  

May  15 

Three  weeks.  .  .  . 

Lime  sulfur  (1—50)  lead  arsenate  (1—50)  

May  23 

Four  weeks    .... 

May  31 

Six  weeks  

Lime  sulfur  (1—50)  lead  arsenate  (1—50)  lime  (1—50).  .  . 

June  13 

Ten  weeks  

Lime  sulfur  (1-50)  lead  arsenate  (1-50)  lime  (1-50).  .  . 

July  11 

(Table  23).    Three  trees  were  left  unsprayed  excepting  for  the  dor- 
mant, cluster  bud,  and  calyx  applications. 

On  July  23,  a  record  was  taken  of  the  amount  of  blotch  on  dropped 
apples  from  the  check  trees  (Table  24).  There  were  no  dropped 
apples  from  the  sprayed  trees  and  careful  observations  of  these  trees 
in  the  latter  part  of  July  testified  to  the  absence  of  blotch  on  the  fruit 
and  foliage.  On  the  unsprayed  trees  the  fruit  and  foliage  chiefly  on 
the  lower  branches  were  infected.  The  orchard  was  given  no  attention 
after  July  and  since  a  serious  outbreak  of  codling  moth,  combined 


1985] 


APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL 


547 


with  black  rot  infection,  occurred  in  August,  much  of  the  fruit  was 
wormy  and  infected  with  black  rot  at  harvest  time.  Undoubtedly  the 
application  of  an  insecticide  in  August  would  have  protected  the  fruit 
against  the  third-brood  codling  moth,  and  its  combination  with  a  fungi- 
cide would  have  safeguarded  the  season 's  growth  against  late  infections 
of  apple  blotch,  had  the  weather  conditions  been  favorable.  In  Sep- 
tember and  October,  and  again  in  March,  1923,  the  season's  twig 
growth  was  examined  for  bark  cankers.  These  were  found  largely 
on  the  water  sprouts,  and  only  on  the  unsprayed  trees.  The  two-, 
three-,  four-,  six-,  and  ten-weeks  spray  schedule,  therefore,  demon- 
strated its  efficiency  in  controlling  apple  blotch  in  this  orchard  in 
1922.  The  exclusive  use  of  lime  sulfur  in  all  of  the  sprays  and  the 

TABLE  24. — NUMBER  OF  DROPPED  BLOTCHED  AND  BLOTCH-FREE  APPLES  FROM  CHECK 
TREES  IN  THE  WEBBER  ORCHARD,  URBANA,  1922 


Total  number 
apples  examined 

Number  blotch- 
free 

Number  blotched 

Slightly 

Severely 

Total 

Percentage 

2  trees,  undetermined 
variety 

860 
326 

741 
121 

97 

77 

22 
128 

119 
205 

13.8 
63 

1  tree,  Ben  Davis.  .  .  . 

absence  of  spray  injury  on  the  fruit  testified  to  the  decided  effective- 
ness of  lime  sulfur  for  the  control  of  apple  blotch. 

In  1922  at  Lilly 

The  main  purpose  of  the  work  at  Lilly  was  to  demonstrate  con- 
trol of  apple  blotch  with  the  proper  spray  schedule.  The  trees  were 
of  the  Northwestern  Greening  variety  on  which  the  disease  was  mak- 
ing serious  progress.  Attempts  by  the  owner  to  control  the  disease 
had  failed  every  season  since  its  first  appearance  in  1917.  In  1921 
the  fruit  from  many  of  these  trees  was  ruined  by  blotch.  Approxi- 
mately twenty-five  trees  were  used  in  the  plan  of  the  experiment  and 
two  of  these  were  not  sprayed. 

The  calyx  spray  was  applied  on  May  5  and  6,  when  75  percent  of 
the  petals  had  fallen.  The  spraying  was  done  with  a  power  sprayer 
and  both  spray  gun  and  rods  were  employed  (Table  25).  The  orchard 
was  visited  on  July  20  and  no  blotch  could  be  found  on  the  fruit  and 
foliage  of  the  sprayed  trees,  but  it  was  common  on  the  unsprayed 
trees.  During  the  period  May  23  to  26,  seventeen  to  twenty-one  days 
after  petal  fall,  heavy  infections  occurred  at  Lilly,  symptoms  of  which 
were  apparent  on  the  fruit  and  foliage  by  June  7  and  8.  The  ab- 
sence of  the  disease  on  the  sprayed  trees  indicated  that  the  two-weeks 
spray  (May  19)  was  applied  at  the  right  time.  The  perfect  results 
demonstrated  the  success  of  the  two-,  three-,  four-,  six-,  and  ten-weeks 
spray  schedule. 


548  BULLETIN    No.   256  [February, 

At  Rome  a  control  demonstration  was  undertaken  on  six  North- 
western Greening  trees  as  a  cheek  on  the  results  at  Lilly.  Local  help 
was  relied  upon  to  apply  the  two-  and  three-weeks  sprays  of  lime  sulfur, 
but  no  accurate  information  could  be  obtained  as  to  the  time  and 
manner  of  these  applications.  The  writer  applied  the  four-weeks 
(June  9)  and  six- weeks  (June  23)  sprays  of  Bordeaux.  No  attention 
was  given  to  the  orchard  after  June  23  (six- weeks  spray)  and  conse- 
quently no  data  were  obtained  on  the  condition  of  the  crop  at  harvest 
time.  There  was  a  considerable  amount  of  disease  on  the  fruit  and 
foliage  as  early  as  June  and  the  infections  were  traced  to  the  condi- 

TABLE  25. — TREATMENT  AND  TIME  OP  APPLICATION  OF  SPRAYS 
AT  LILLY  ORCHARDS,  1922 


Application 

Treatment                                    , 

Time  of  application 

Lime  sulfur  (1—40)  lead  arsenate  (1—50)  

May  19 

Lime  sulfur  (1—40)  lead  arsenate  (1—50)  

May  26 

Lime  sulfur  (1-40)  lead  arsenate  (1-59)  

June  2 

Bordeaux  (3-4-50)  lead  arsenate  (1-50)    

June  16 

Bordeaux  (3—4-50)  lead  arsenate  (1-50)    

July  20 

tions  of  May  23  to  27,  or  two  and  one-half  to  three  weeks  after  petal 
fall.  It  was  evident  that  the  early  infections  were  not  suppressed, 
altho  spraying  had  the  effect  of  reducing  the  amount  of  infection 
more  than  in  previous  years. 

SUMMER  SPRAYING:    CONCLUSIONS 

While  the  spraying  experiments  have  not  been  extensive  and  on 
a  large  scale,  the  results,  together  with  the  knowledge  of  the  life  his- 
tory of  the  fungus,  make  it  possible  to  arrive  at  recommendations  for 
the  successful  control  of  the  disease  with  sprays. 

The  infections  are  most  frequent  in  the  spring  and  consequently 
the  application  of  sprays  must  be  frequent  at  this  time  of  the  season 
in  order  to  keep  the  growth  protected,  and  as  the  summers  are  usually 
dry,  applications  are  necessary  only  at  wide  intervals.  Since  the  pri- 
mary infections  usually  occur  from  two  to  three  weeks  after  the  petals 
have  fallen,  the  first  spray  for  apple  blotch  must  be  applied  between  ten 
days  and  two  weeks  after  petal  fall  and  not  later  than  two  weeks  after 
petal  fall.  This  recommendation  applies  to  all  varieties  of  apples.  It 
is  the  critical  application  of  the  season  and  the  production  of  blotch- 
free  apples  depends  upon  the  timely  and  thoro  application  of  the 
first  spray.  The  suppression  of  the  first  infections  is  significant  in 
that  it  prevents  the  multiplication  of  the  disease  in  the  orchard. 

In  addition  to  the  two-weeks  spray,  later  sprays  must  be  applied 
in  the  order  of  three,  four,  six,  ten,  and  fifteen  weeks  after  the  petals 
have  fallen,  the  last  two  applications  conforming  to  the  period  of  the 


APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  549 

second-  and  third-brood  codling  moth.  They  are  particularly  necessary 
for  susceptible  fall  and  winter  varieties  of  apples.  In  view  of  the 
duration  of  the  infection  period  the  need  of  so  many  sprays  is  obvious. 
Since  the  spraying  with  arsenate  of  lead  for  the  second-  and  third- 
brood  codling  moth  is  generally  practiced,  the  addition  of  a  fungicide 
at  these  intervals  is  only  a  matter  of  some  small  expense  compared  with 
the  value  of  the  returns.  The  two-,  four-,  six-,  ten-weeks  schedule  of 
Beach5  of  hydrated  lime-Bordeaux  (3-5-50),  the  preliminary  schedule 
of  Rolfs72  of  Bordeaux  at  two  and  four  to  five  weeks  and  arsenate  of 
lead  at  seven  to  eight  weeks  after  the  fall  of  the  petals  cannot  be 
recommended  in  Illinois  since  the  period  between  the  two-  and  four- 
weeks  applications  is  entirely  too  long  and  since  no  provision  is  made 
for  late  infections,  and  further  because  under  Illinois  conditions  Bor- 
deaux cannot  safely  be  used  ordinarily  at  two  weeks  after  the  fall  of 
the  petals.  Likewise,  the  two-,  three-,  four-,  five-,  seven-,  ten-weeks 
schedule  of  Brock16  of  early  applications  of  lime  sulfur  and  summer 
applications  of  Bordeaux,  makes  no  provision  for  late  seasonal  infec- 
tions. It  is  more  profitable,  and  as  effective,  to  omit  the  five-  and 
seven-weeks  applications  and  to  make  an  application  at  six  weeks  after 
petal  fall,  especially  for  early  varieties  like  the  Duchess,  Benoni,  and 
Yellow  Transparent,  which  usually  require  from  nine  to  ten  weeks 
to  mature.  Ordinarily,  the  conditions  are  dry  in  Illinois  after  four 
weeks  after  petal  fall  and  with  the  protection  afforded  by  the  two-, 
three-,  and  four-weeks  applications  it  is  unnecessary  to  make  the  next 
application  until  six  weeks  after  petal  fall.  The  six-weeks  applica- 
tion for  early  varieties  also  is  as  effective  as  the  seven-weeks  applica- 
tion for  the  protection  of  the  growth  until  harvest. 

The  time  of  the  applications  is  of  more  importance  than  the  nature 
of  the  spray.  Lime  sulfur  and  Bordeaux  are  still  considered  the 
standard  and  dependable  sprays  for  Illinois  orchards.  They  have 
been  employed  repeatedly  by  the  writer  in  the  control  of  apple  blotch 
with  equal  and  highly  favorable  results,  thus  verifying  earlier  litera- 
ture. However,  because  of  the  greater  adhesive  quality  and  toxicity 
of  Bordeaux  this  fungicide  is  the  better  spray  for  long  periods; 
nevertheless,  with  the  schedules  employed,  lime  sulfur  alone  has  given 
perfectly  satisfactory  results.  Both  of  these  fungicides  should  be 
employed  in  the  proportions  recommended  under  Illinois  conditions; 
namely,  lime  sulfur  32°  Baume,  1-40  and  Bordeaux  3-4-50.  The  se- 
lection of  either  one  of  these  fungicides  for  any  particular  applica- 
tion depends  upon  the  variety  and  the  prevailing  weather  conditions. 
The  moist  cool  weather  of  the  spring  months  in  Illinois  prohibits  the 
use  of  Bordeaux  and  the  hot  dry  weather  of  the  summer  prohibits  the 
use  of  lime  sulfur.  The  general  fungicidal  effect  without  burning  can 
successfully  be  obtained  by  employing  lime  sulfur  for  the  first  one  or 
two  blotch  sprays — at  two  weeks  and  three  weeks  after  petal  fall— 


550  BULLETIN   No.   256  [February, 

and  Bordeaux  for  the  remaining  applications.  The  results  of  the 
writer,  and  those  of  growers,  with  hydrated  lime-Bordeaux  have  dem- 
onstrated that  its  efficiency  for  apple  blotch  control  is  equal  to  that 
of  the  ordinary  Bordeaux  prepared  from  slaked  lime  and  that  its 
use  also  must  be  restricted  to  applications  later  than  two  and  three 
weeks  after  petal  fall. 

The  success  in  controlling  apple  blotch  lies  in  keeping  the  surface 
of  the  fruit,  foliage,  and  growing  twigs  covered  with  spray  during 
the  growing  season.  The  failures  have  been,  and  are,  due  to  delay 
in  the  first  application,  and  to  making  the  applications  too  far  apart. 
A  power  sprayer  furnishing  pressure  of  225  to  300  pounds  is  neces- 
sary to  apply  the  spray  forcibly  (as  a  fine  mist),  in  order  to  reach 
every  portion  of  the  tree. 


OTHER  ASPECTS  OF  CONTROL 
Soil  Treatments 

The  results  in  Illinois  from  fertilization  of  blotch  infected  orchards 
with  sodium  nitrate  or  ammonium  sulfate  gave  no  evidence  of  in- 
creased resistance  of  the  bark  to  apple  blotch  nor  any  reduction  in  the 
amount  of  the  disease.  Rather  the  opposite  was  true,  since  the  in- 
creased succulence  of  the  growth  as  the  result  of  soil  treatments  was 
favorable  for  infection  and  for  the  growth  of  the  fungus. 

Fertilization,  however,  is  necessary  for  the  rejuvenation  of  badly 
infected  trees  and  the  spraying  program  for  the  control  of  blotch 
in  badly  infected  orchards  should  include  some  attention  to  the  needs 
of  the  soil,  cultivation  and  the  use  of  nitrogenous  fertilizers  being 
desirable.  Since  the  trees  respond  actively  to  soil  treatments  they 
must  be  sprayed  regularly  in  accordance  with  the  recommended  spray 
schedule  in  order  to  maintain  growth  free  of  infection.  Following 
such  a  procedure,  some  varieties  of  trees  may  eventually  be  freed  of 
bark  cankers. 

Pruning 

The  removal  of  infected  branches  and  twigs,  primarily  to  decrease 
the  amount  of  apple  blotch  infection,  is  impracticable  and  seems  never 
to  have  been  adopted  by  growers.  The  practice  causes  excessive  prun- 
ing and  involves  much  time  and  expense. 

Pruning  for  the  .purpose  of  removing  dead  wood  and  crossed 
branches,  thus  opening  the  trees  to  uniform  distribution  of  the  spray, 
is  a  worthy  practice.  The  succulent  growth  which  may  be  induced 
as  the  result  of  this  pruning  can  be  maintained  free  of  infection 
by  spraying. 


1925]  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  551 

Surgery 

Even  tho  histology  of  the  bark  cankers  shows  that  removal  of  the 
fungus  from  nursery  stock  or  young  trees  in  the  orchard  by  cutting 
is  a  simple  operation,  the  method  cannot  be  recommended  since  the 
cankers  are  frequently  too  numerous,  and  often  too  small  to  be  de- 
tected by  the  growers.  The  method  is  tedious  and  impracticable,  re- 
quiring reinspection  of  the  trees  and  repetition  of  the  process,  for 
which  reasons  growers  cannot  be  induced  to  undertake  the  practice. 

It  is  more  desirable  to  reject  diseased  trees  from  the  nursery  and 
thus  keep  the  fungus  from  the  orchard. 

Protective  and  Preventive  Measures 

The  means  of  avoiding  apple  blotch  in  the  young  orchard  rest 
largely  with  the  nurserymen.  Nurserymen  grow  and  sometimes  sell 
diseased  trees,  and  it  is  known  that  they  have  received  blotch-infected 
apple  seedlings  from  localities  where  apple  blotch  is  seriously  preva- 
lent. It  is  desirable,  therefore,  that  measures  be  enforced  in  the 
separate  states  that  will  insure  rigid  inspection  of  all  apple  seedlings 
and  the  exclusion  from  shipment  of  all  stock  that  is  infected. 

In  order  to  insure  disease-free  apple  seedlings  the  seedling  growers 
should  be  required  to  spray  the  nursery  rows  during  the  growing 
season.  This  is  a  protective  measure  for  the  thousands  of  growers 
and  nurserymen  in  the  United  States  who  are  necessarily  dependent 
for  their  stocks  upon  the  American  growers  of  seedlings. 

In  the  second  place,  local  nurserymen  must  protect  themselves 
against  the  receipt  of  infected  seedling  stock  from  the  seedling  growers, 
and  the  steps  which  they  may  wisely  take  will  consist  of  rigid  inspec- 
tion of  the  seedlings  and  the  rejection  of  all  infested  stock  intended 
for  budding.  If  the  seedling  stock  is  used  for  grafting  there  is  no 
danger  of  distributing  the  disease  provided  healthy  scions  are  em- 
ployed. Unless  it  is  possible  to  obtain  blotch-free  American  grown 
apple  seedlings,  it  may  be  wise  for  nurserymen  to  use  foreign-grown 
seedling  stock. 

Local  nurserymen  must  be  cautious  in  the  selection  of  buds  and 
scions,  and  as  a  measure  of  safety  should  select  them  from  trees  which 
they  know  are  free  of  blotch  cankers.  As  long  as  spraying  is  directed 
primarily  for  the  protection  of  fruit,  infections  of  the  bark  will  occur ; 
thus  the  danger  of  selecting  diseased  buds  and  scions  is  evident, 
especially  among  early  varieties,  such  as  Yellow  Transparent,  Benoni, 
and  Duchess.  Since  the  fungus  persists  for  many  years  in  the  bark 
of  some  varieties,  the  policy  of  destroying  cankered  trees  in  the 
nursery  rows  should  be  followed  rigidly  in  order  to  safeguard  other 
trees  from  infection. 


552  BULLETIN   No.   256  [February, 

The  growers  can  save  themselves  much  expense  and  unnecessary 
losses  later  in  the  fruiting  period  of  the  trees  by  carefully  examining 
the  young  trees  upon  receipt  from  the  nurseries  and  rejecting  those 
which  show  evidence  of  cankers.  The  planting  of  healthy  trees 
is  strongly  recommended  and  is  most  economical  in  the  end.  If  the 
grower  is  not  sure  of  obtaining  blotch-free  trees  from  nurserymen  in 
the  blotch  area  it  may  be  wise  for  him  to  buy  from  nurseries  in  states 
where  the  disease  is  known  not  to  exist. 

Selection  and  Location  of  Varieties 

It  is  imperative  to  select  varieties  which  are  bark-resistant,  and  to 
plant  them  at  a  distance  from  bark-susceptible  varieties. 

Growers  are  divided  in  their  opinions  as  to  the  selection  of  vari- 
eties, even  among  those  seriously  susceptible  to  fungi.  In  the  central 
and  western  sections  of  the  state,  commercial  growers  still  favor  the 
Ben  Davis  in  spite  of  the  fact  that  all  our  serious  apple  maladies  are 
common  on  this  variety,  blotch,  blister  canker,  and  scab  being  espe- 
cially so.  In  southern  Illinois,  owing  to  this  susceptibility,  the  Ben 
Davis  has  become  unpopular  and  is  no  longer  planted.  Likewise,  there 
is  difference  of  opinion  in  regard  to  the  Duchess  variety,  which  in 
Illinois  ranks  among  those  most  susceptible  to  apple  blotch ;  yet  some 
growers  realize  that  control  is  possible  and  they  feel  that  the  high 
market  value  of  this  apple  warrants  planting  it.  It  must  be  empha- 
sized, however,  that  the  more  susceptible  the  variety  the  more  ex- 
pensive its  culture,  and  unless  growers  feel  that  they  can  care  for 
the  trees  in  the  proper  manner  they  should  select  varieties  which  are 
relatively  bark-resistant,  and  by  all  means  reject  varieties  very  sus- 
ceptible to  bark  infection  (Table  14). 

The  writer  opposes  the  selection  of  bark-susceptible  varieties,  since 
it  is  obvious  that  the  control  of  insects  and  fungi  is  a  serious  problem 
to  be  avoided  when  possible.  However,  if  a  grower  insists  upon  plant- 
ing these  varieties  he  should  separate  them  well  from  resistant  ones 
so  that  he  may  concentrate  his  spraying,  especially  during  the  busy 
seasons,  within  a  relatively  small  area  and  thus  save  time  and  labor. 

RECOMMENDATIONS  FOR  CONTROL 

The  recommendations  for  the  control  of  apple  blotch  may  be  con- 
sidered under  two  headings — pruning  and  spraying. 

In  pruning,  aim  to  remove  crowded  and  dead  branches  in  accord- 
ance with  general  pruning  methods  so  that  the  sprays  may  reach 
every  apple.  Remove  surplus  water  sprouts:  they  are  particularly 
undesirable  since  they  are  very  susceptible  to  infection.  In  renovat- 


1925]  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  553 

ing  the  orchard,  leave  only  those  water  sprouts  which  are  expected  to 
be  of  some  use  in  developing  the  framework  of  the  trees. 

All  pruning  should  be  done  prior  to  the  dormant  spray. 

Trees  must  be  sprayed  uniformly.  The  practice  of  applying  the 
spray  from  one  side  of  the  tree  with  the  wind,  or  from  one  side  of  the 
tree  for  one  application  and  from  the  opposite  side  for  the  succeed- 
ing application,  cannot  be  recommended.  Either  guns  or  rods  may 
be  employed  with  disc  nozzles  having  small  openings.  High  pres- 
sures of  225  to  300  pounds  are  desirable  to  force  the  spray  into  the 
trees  as  a  fine  mist.  It  is  necessary  to  apply  the  sprays  on  time  with 
reference  to  the  time  the  petals  have  fallen  (75  percent  fallen)  and 
in  accordance  with  the  following  schedule. 

Dormant  Spray. — This  application  should  be  made  late  in  the  dor- 
mant season,  preferably  when  the  tips  of  the  buds  are  showing  green 
(delayed  dormant),  using  commercial  lime  sulfur  32  or  33°  Baume 
in  the  proportion  of  1  gallon  of  lime  sulfur  to  8  gallons  of  water,  or 
copper  sulfate  in  the  proportion  of  1  pound  to  10  gallons  of  water. 
Spray  thoroly  and  if  severely  cankered,  drench  the  trees. 

First  Blotch  Spray. — Apply  a  few  days  earlier  than  two  weeks 
after  petal  fall  and  complete  the  application  by  two  weeks  after  petal 
fall.  Use  lime  sulfur  in  the  proportion  of  1  gallon  of  lime  sulfur  to 
50  gallons  of  water;  and  for  every  50  gallons  of  spray  solution,  add 
1  pound  of  powdered  arsenate  of  lead. 

Second  Blotch  Spray. — At  three  weeks  after  the  fall  of  the  petals, 
use  the  same  treatment  as  for  the  first  blotch  spray. 

Third  Blotch  Spray. — At  four  weeks  after  the  fall  of  the  petals, 
use  Bordeaux  in  the  proportion  of  3  pounds  of  copper  sulfate,  and 
4  pounds  of  slaked  lime*  to  50  gallons  of  water. 

Fourth  Blotch  Spray. — At  six  weeks  after  the  fall  of  the  petals, 
use  the  same  treatment  as  for  the  third  blotch  spray. 

Fifth  Blotch  Spray. — At  nine  or  ten  weeks  after  the  fall  of  the 
petals,  use  the  same  treatment  as  for  the  third  blotch  spray,  adding 
1  pound  of  powdered  arsenate  of  lead  for  every  50  gallons  of  spray. 
The  time  of  this  application  corresponds  to  that  of  the  second-brood 
codling  moth. 

Sixth  Blotch  Spray. — Apply  in  the  middle  of  August.  The  time 
of  this  application  corresponds  to  that  of  the  third-brood  codling  moth. 
Use  the  same  materials  as  for  the  fifth  blotch  spray.  This  is  the  last 
spray  for  apple  blotch  and  is  intended  to  protect  the  fruit  of  late 
varieties  against  late  infections.  Its  application  in  some  seasons  for 
blotch  may  not  be  necessary,  depending  upon  the  weather. 


•  If  hydrated  lime  is  used  instead  of  rock  lime  use  5  pounds  to  50  gallons. 


554  BULLETIN   No.   256  [February, 

For  early  varieties,  such  as  Yellow  Transparent,  Duchess,  and 
sometimes  Benoni,  only  the  two-,  three-,  four-,  and  six-weeks  applica- 
tions are  necessary  to  protect  the  fruit  until  harvest.  Usually  for 
the  Benoni  and  other  varieties  that  are  harvested  around  ten  weeks 
after  blooming  an  application  eight  weeks  after  the  fall  of  petals 
is  desirable  in  seriously  cankered  orchards.  For  late  summer  vari- 
eties the  ten-weeks  spray  is  desirable  for  blotch,  as  well  as  for  the 
second-brood  codling  moth.  It  is  impossible  to  make  any  definite 
recommendations  of  late  sprays  for  every  orchard  and  every  section 
of  Illinois.  The  need  of  these  late  sprays  should  be  determined  by 
the  grower,  and  his  decision  should  be  guided  by  the  weather  peculiar 
to  his  section  and  by  the  amount  of  infection  in  the  orchard. 

In  addition  to  pruning  and  spraying,  soil  treatments  in  the  form 
of  cultivation  and  fertilization  are  particularly  necessary  in  old  and 
weakened  orchards. 

In  planting  the  orchard,  varieties  should  be  selected  which  are 
relatively  resistant  to  bark  infections.  If  bark-susceptible  varieties  of 
high  commercial  value  are  desirable  they  should  be  planted  at  a  dis- 
tance from  bark-resistant  varieties. 

All  infected  trees  from  the  nursery  should  be  rejected. 

LITERATURE  CITED 

1.  ADAMS,  J.  F.    Notes  on  plant  diseases  in  Pennsylvania.     Pa.  State  College, 

Ann.  Rpt.  Pt.  II;    Agr.  Exp.  Sta.,  Ann.  Ept.  1916-17.     329-330.     1919. 

2.  ALLESCHEE,  A.     Babenhorst,  Kryptogamen-Flora  von  Deutschland,  Oesterr. 

und  der  Schweiz.     1.     Pt.  6.     Fungi  imperfecti.     12-15,  169-172.     1901. 

3.  ANDERSON,  H.  W.     The  northward  advance  of  apple  blotch  and  how  it  may 

be  checked.    Trans.  111.  State  Hort.  Soc.,  n.s.,  54,  234-237.     1920. 

4.  BALLOU,  F.  H.,  and  LEWIS,  I.  P.     Spraying .  experiments  in  southeastern 

Ohio.     Ohio  Agr.  Exp.  Sta.  Mo.  Bui.  8,  47-50.     1923. 

5.  BEACH,  F.  H.     The  control  of  apple  blotch.     Ohio   State  University  Agr. 

Ext.  Bui.  15,  No.  8.     1919-20. 

6.    —     Results  of  apple  blotch  control  in  southern  Ohio.     Trans.  Ind. 

Hort.  Soc.,  1919,  63-72.    1920. 

7.    —    Results  of  apple  blotch  control  in  southern  Ohio.     Hoosier  Hort., 

2,  3-9.     1920. 

8.  BLAIR,  J.  C.,  PICKETT,  B.  S.,  WATKINS,  O.  S.,  RUTH,  W.  A.,  FOGLESONG, 

L.    E.,   and   GUNDERSON,   A.   J.      Field   experiments   in   spraying   apple 
orchards.    111.  Agr.  Exp.  Sta.  Bui.  185.     1916. 

9.  BROCK,  W.  S.     Dusting  vs.  spraying.     Trans.  Ind.  Hort.  Soc.,  1916,  69-73. 

1917. 

10.  -  -    Apple  blotch  control.    Trans.  Ind.  Hort.  Soc.,  1918,  103-111.    1919. 

11.    Five   years   experimental   work  in   dusting  apples.     Trans.   Ind. 

Hort.  Soc.,  1918,  150-156.     1919. 

12.   Spraying  and  dusting  experiments  of  1918.     Trans.  111.   State 

Hort.  Soc.,  n.s.,  52,  132-136.     1918. 

13.   Five  years  experimental  work  in  dusting  apples.     Hoosier  Hort., 

1,  11-13.    1919. 

14.  -  The  report  of  spraying  investigations  for  the  season  of  1919. 

Trans.  111.  State  Hort.  Soc.,  n.s.,  53,  130-137.    1919. 

15.    —    A  report  of  field  experimental  work  in  1920.     Trans.  111.  State 

Hort.  Soc.,  n.s.,  54,  184-190.     1920. 


1925}  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  555 

16.    The  control  of  blotch  and  scale.    Trans.  HI.  State  Hort.  Soc.,  n.s., 

56,  432-446.     1922. 

17.  CLINTON,  G.  P.    Apple  rots  in  Illinois.    111.  Agr.  Exp.  Sta.  Bui.  69,  190-192. 

1902. 

18.  COONS,  G.  H.     Factors  involved  in  the  growth  and  the  pycnidium  formation 

of  Plenodomus  fuscomaculans.     Jour.  Agr.  Ees.  5,  713-769.     1916. 

19.    and  LEVINE,  E.     The  relation  of  light  to  pycnidium  formation  in 

the  Sphaeropsidales.     Mich.  Acad.  Sci.,  Ann.  Rpt.  1920,  209-213.     1921. 

20.  COOPER,  J.  E.     Spraying  experiments  in  Nebraska.     Nebr.  Agr.  Exp.  Sta. 

Ees.  Bui.  10,  51-62.     1917. 

21.    —     Studies  of  the  etiology  and  control  of  blister  canker  of  apple 

trees.     Nebr.  Agr.  Exp.  Sta.  Ees.  Bui.  12.     1917. 

22.  COOK,  M.  T.     Eeport  of  the  plant  pathologist.    N.  J.  Agr.  Exp.  Sta.,  Ann. 

Ept.  1912,  517.     1913. 

23.  CRANDALL,  C.  S.    Eelative  merits  of  liquid  and  dust  spray.    Trans.  111.  State 

Hort.  Soc.,  n.s.,  39,  547-565.     1905. 

24.    •     Eelative  merits  of  liquid  and  dust  applications.     111.  Agr.  Exp. 

Sta.  Bui.  106,  217-218.     1906. 

25.  DICKENS,  A.,  and  HEADLEE,  T.  J.    Spraying  the  apple  orchard.    Kans.  Agr. 

Exp.  Sta.  Bui.  174,  283-284.     1911. 

26.  DOUGLASS,  B.  W.     Some  diseases  of  the  apple.     Trans.  Ind.   Hort.   Soc., 

92-101.     1909. 

27.    Orchard  and  garden.     Federal  Publishing  Co.,  Indianapolis,  Ind., 

85-86.     1918. 

28.  -  —     War  and  the  fruit  grower.     Country  Gent.,  Sept.  14,  1918.     7. 

29.  -  — •     Fruit  diseases  of  1919.     Country  Gent.,  Apr.  17,  1920.     20. 

.30.    ELLIS,  J.  B.,  and  EVERHART,  B.  M.     New  species  of  fungi  from  various 
localities.    Proc.  Acad.  Nat.  Sci.  Phila.,  1895,  430.    1896. 

31.  FAUROT,  F.  W.     Eeport  on  fungous  diseases  occurring  on  cultivated  fruits 

during  the  season  of  1902.     Mo.  Fruit  Exp.  Sta.  Bui.  6,  7-8.     1903. 

32.  FOGLESONG,  L.  E.    Eesults  from  spraying  experiments,  1909,  in  Pike  County. 

Trans.  111.  State  Hort.  Soc.,  n.s.,  43,  365-371.     1909. 

33.  FROMME,  F.  D.,  and  EALSTON,  G.  S.    Dusting  experiments  in  peach  and  apple 

orchards.    Va.  Agr.  Exp.  Sta.  Bui.  223.    1919. 

34.  FROMME,  F.  D.,  EALSTON,  G.  S.,  and  EHEART,  J.  F.    Dusting  experiments  in 

peach  and  apple  orchards  in  1920.     Va.  Agr.  Exp.  Sta.  Bui.  224.     1921. 

35.  GARDNER,  M.  W.    Origin  of  apple  blotch  cankers.    Phytopath.    12,  55.    1922. 

36.    and  JACKSON,  H.  S.    New  aspects  of  apple  blotch  control.    Phyto- 
path.   13,  44.    1923. 

37.  GARMAN,  H.    Spraying  apple  trees.    Ky.  Agr.  Exp.  Sta.  Bui.  133,  65.    1908. 

38.  GIDDINGS,  N.  J.     Orchard  spraying  vs.  dusting.     W.  Va.  Agr.  Exp.  Sta.  Bui. 

167.     1918. 

39.  GLOYER,  W.  A.     The  occurrence  of  apple  blotch  in  Ohio.     Ohio.  Nat.  11,  6, 

334-336.     1911. 

40.  GUBA,  E.  F.     The  effect  of  dormant  sprays  on  the  control  of  apple  blotch. 

Sci.,  n.s.,  53,  484-485.     1921. 

41.    The  nature  and  control  of  apple  blotch.     111.  Agriculturist  26, 

197-198.     1922. 

42.  GUNDERSON,  A.  J.     Spray  schedules  and  formulas  for  apples  and  peaches  in 

southern  Illinois.     Trans.  111.  State  Hort.  Soc.,  n.s.,  49,  440-452.     1915. 

43.  —       —     Spraying  experiments  in   1916  for  the  control  of  apple  blotch. 

Trans.  111.  State  Hort.  Soc.,  n.s.,  50,  248-251.     1916. 

44.    Spraying   for   the  control   of   apple  blotch  in   southern   Illinois. 

Trans.  111.  State  Hort.  Soc.,  n.s.,  52,  83-86.     1918. 

45.    •     Field  experiments  for  spraying  apple  orchards  for  the  control  of 

apple  blotch.    111.  Agr.  Exp.  Sta.  Bui.  222.     1919. 

46.  HEWITT,  J.  L.     How  to  control  scab  and  blotch  of  apple.     Ark.  Agr.  Exp. 

Sta.  Circ.  7.     1911. 

47.    and  HAYHURST,  P.     Diseases  of  apple  trees  and  fruit  caused  by 

fungi  and  insects.    Ark.  Agr.  Exp.  Sta.  Bui.  109,  421-422.     1911. 


556  BULLETIN   No.   256  [February, 

48.  HOHNEL,    F.    VON.     Uber    Phyllostictina    Murrayae    Sydow.      Mykologische 

Fragmente  332.     Ann.  Mycol.     18,  93-95.     1920. 

49.  JACZEWSKI,  A.  de.     Uber  die  Pilze,  welche  die  Krankheit  der  Weinreben 

"Black  Rot"  verursachen.     Ztschr.  Pflanzenkrank.     10,  257-267.     1900. 

50.  LEVINE,  E.     Light  and  pycnidia  formation  in  the  Sphaeropsidales.     Mich. 

Acad.  Sci.,  Ann.  Ept.  1915,  134-135.     1915. 

51.  LEWIS,  D.  E.  The  control  of  apple  blotch.     Kans.  Agr.  Exp.  Sta.  Bui.  196. 

1913. 

52.  MORRIS,  B.  S.,  and  NICHOLSON,  J.  F.     Orchard  spraying.     Okla.  Agr.  Exp. 

Sta.  Bui.  76.     1908. 

53.  McCORMACK,  E.  F.     Fungous  diseases  of  the  apple.     State  Entomologist  of 

Ind.,  Ann.  Rpt.  1909-10,  128-165.     1910. 

54.  OHIO   AGRICULTURAL  EXPERIMENT   STATION.     Apple  blotch   control   proves 

successful.    Ohio  Agr.  Exp.  Sta.  Mo.  Bui.    4,  11,  344.     1919. 

55.  OKLAHOMA  AGRICULTURAL  EXPERIMENT  STATION.     Report  of  Horticultural 

Department.     Apple  Blotch.     Ann.  Ept.     1922,  21-22. 

56.  ORTON,  W.  A.,  and  AMES,  A.     Plant  diseases  in  1907.     U.  S.  Dept.  Agr., 

Yearbook  1907,  577-589.     1908. 

57.    Plant  diseases  in  1908.    U.  S.  Dept.  Agr.,  Yearbook  1908,  533-538. 

1909. 

58.  OSKAMP,  J.     Some  newer  phases   of  disease   and  insect   control.     Double 

strength  lime  sulphur.     Trans.  Ind.  State  Hort.  Soe.  41,  33-42.     1918. 

59.  PENNSYLVANIA  AGRICULTURAL  EXPERIMENT  STATION.    Annual  report  of  the 

director  for  the  year  ending  June  30,  1922.    Report  on  projects.    Botany 
and  plant  pathology.    Pa.  Agr.  Exp.  Sta.  Bui.  176,  12.    1922. 

60.  PERRAUD,  J.    Sur  les  formes  de  conservation  et  de  reproduction  du  black  rot. 

Compt.  Rend.,  Acad.  Sci.  (Paris),  128,  1249-1251.     1899. 

61.  PRILLIEUX,    E.      Production    de    pSritheces    de    Physalospora    Bidwelli    au 

printemps  sur  les  grains  de  raisins  attaques  1'annee  precedente  par  le 
black  rot.    Bui.  Soc.  Mycol.  France,  4,  59-61.    1888. 

62.  PRUNET,  A.    Les  formes  du  parasite  du  black  rot,  de  1'automne  au  printemps. 

Compt.  Rend.,  Acad.  Sci.  (Paris),  124,  250-252.     1897. 

63.  PURDUE    (INDIANA)    AGRICULTURAL    EXPERIMENT    STATION.      Miscellaneous 

plant  disease  studies.     Ann.  Rpt.  1919,  24-25. 

64.  Foot  rot  of  wheat.     Ann.  Rpt.  1920,  17. 

65.  RATHAY,  E.     Der  Black  Rot.     Ztschr.  Pflanzenkrank.    1.    306-314.     1891. 

66.  REDDICK,  D.     The  black  rot  disease  of  grapes.     N.  Y.  (Cornell)  Agr.  Exp. 

Sta.  Bui.  293.    1911. 

67.  ROBERTS,  J.  W.    Apple  blotch  and  its  control.     U.  S.  Dept.  Agr.  Bui.  534. 

3917. 

68.    Apple  blotch  and  bitter  rot  cankers.     Phytopath.     10,  353-357. 

1920. 

69.    Apple  blotch  and  bitter  rot  and  their  control.     Proc.  Tenn.  State 

Hort.  Soc.  16,  38-45.    1921. 

70. Plum  blotch,  a  serious  disease  of  the  Japanese  plum,  caused  by 

Phyllosticta  congesta.     Jour.  Agr.  Res.  22,  365-370.     1921. 

71.  ROLFS,  F.  M.     Report  of  Horticultural  Department.     Adams  project  No.  8. 

Development  of  fruit  buds.    Okla.  Agr.  Exp.  Sta.,  Ann.  Rpt.  1918,  43-45. 

72.    Report  of  Horticultural  Department.     Adams  project  No.  8.    De- 
velopment of  fruit  buds.     Okla.  Agr.  Exp.  Sta.,  Ann.  Rpt.  1919,  45-47. 

73.  —     Report  of  Horticultural  Department.    Okla.  Agr.  Exp.  Sta.,  Ann. 
Rpt.  1920.     49. 

74.  SACCARDO,  P.  A.     Sylloge  fungorum  omnium  huscusque  cognitorum.     Padua. 

14,  849.    1899. 

75.  SCOTT,  W.  M.     The  use  of  lime  sulfur  sprays  in  the  summer  spraying  of 

Virginia  apple  orchards.     Va.  Agr.  Exp.  Sta.  Bui.  188.     1910. 

76. The  substitution  of  lime  sulfur  preparations  for  Bordeaux  mix- 
ture in  the  treatment  of  apple  diseases.  U.  S.  Dept.  Agr.,  Bur.  Plant 
Indus.  Circ.  54.  1910. 

77.  -  and  QUAINTANCE,  A.  L.  Spraying  for  apple  diseases  and  codling 

moth  in  the  Ozarks.  U.  S.  Dept.  Agr.,  Farmers'  Bui.  283,  14-18.  1907. 


1925}  APPLE  BLOTCH:    ITS  ETIOLOGY  AND  CONTROL  557 

78. and  BORER,  J.  B.  The  relation  of  twig  cankers  to  the  Phyllosticta 

apple  blotch.  Proc.  Benton  County,  Ark.,  Hort.  Soc.,  1-6.  1907. 

79. •  Apple  blotch,  a  serious  disease  of  southern  orchards.  TL  S. 

Dept.  Agr.,  Bur.  Plant  Indus.  Bui.  144.  1909. 

80.  SCRIBNER,  F.  L.    New  observations  on  the  fungus  of  the  black  rot  of  grapes. 

Proc.  Soc.  Prom.  Agr.  Sci.  9,  68-72.     1888. 

81.  SEAVER,  F.  J.     Phyllostictales.     Phyllostictaceae    (pars.)    N.   A.   Flora.   6, 

Pt.  1,  41.    1922. 

82.  SELBY,  A.  D.     Brief  report  on  plant  diseases  in  Ohio  for  1910.     Columbus 

Hort.  Soc.,  Ann.  Ept.  1910,  13-19.    1911. 

83.    •    Apple  blotch,  a  serious  fruit  disease.     Ohio  Agr.  Exp.  Sta.  Bui. 

333.     1919. 

84.  SHEAR,  C.  L.    Cranberry  diseases.    U.  S.  Dept.  Agr.,  Bur.  Plant  Indus.  Bui. 

110,  14-26.     1907. 

85.    •     Life   histories    and    undescribed    genera    and    species    of    fungi. 

Mycol.  15,  120-131.    1923. 

86.  SHELDON,  J.  L.    Concerning  the  relationship  of  Phyllosticta  solitaria  to  the 

fruit  blotch  of  apples.     Science,  n.s.  26",  183-185.    1907. 

87.  STEVENS,  F.  L.     Two  interesting  apple  fungi.     Science,  n.s.  26,   724-725. 

1907. 

88.    and  HA.LL,  J.  G.    Notes  on  plant  diseases  occurring  in  North  Caro- 
lina.    N.  C.  Agr.  Exp.   Sta.,  Ann.   Rpt.  1907-08,  67-68.     1909. 

89.  STEWART,  V.  B.     The  leaf  spot  disease  of  horse  chestnut.     Phytopath.  6, 

5-19.     1916. 

90.  STOVER,  W.  G.,  BEACH,  F.  H.,  and  PARKS,  T.  H.     Results  of  spraying  the 

apple  for  blotch  in  Ohio  in  1919.    Phytopath.  10,  58.    1920. 

91.  SYDOW,  H.  P.,  et  BUTLER,  E.  J.     Fungi  Indiae  orientalis.    Ann.  Mycol.  14, 

185-186.     1916, 

92.  UNDERWOOD,  L.  M.     Report  of  the  Botanical  Division  of  the  Indiana  State 

Biological  Survey  for  1894.    Proc.  Ind.  Acad.  Sci.,  1894,  144-156.    1895. 

93.  U.  S.  DEPARTMENT  OF  AGRICULTURE,  BUREAU  OF  PLANT  INDUSTRY.    Summary 

of  plant  diseases  in  the  United  States  in  1918.    Diseases  of  fruit  crops. 
Plant  Disease  Bui.,  Supplement  1.     1919. 

94. Crop  losses  from  plant  diseases,  1918.     Plant  Disease  Bui.,  Sup- 
plement 6.    1919. 

95. Diseases  of  fruit  crops  in  the  United  States  in  1919.     Plant  Dis- 
ease Bui.,  Supplement  9.    1920. 

96.  -      Crop  losses  from  plant  diseases  in  the  United  States  in   1919. 

Plant  Disease  Bui.,  Supplement  12.     1920. 

97.  -    Diseases  of  fruit  crops  in  the  United  States  in  1920.     Plant  Dis- 

ease Bui.,  Supplement  14.     1921. 

98.  -          —     Crop  losses  from  plant  diseases  in  the  United   States  in  1920. 

Plant  Disease  Bui.,  Supplement  18.    1921. 

99.    Diseases  of  fruit  and  nut  crops  in  the  United  States  in  1921. 

Plant  Disease  Bui.,  Supplement  20.     1922. 

100.    Crop   losses   from   plant  diseases   in   the   United   States    in    1921. 

Plant  Disease  Bui.,  Supplement  24.     1922. 

101.    Disease  of   fruit  and  nut  crops  in  the  United  States   in   1922. 

Plant  Disease  Bui.,  Supplement  28.    1923. 

102.  -     Crop  losses  from  plant   diseases  in   the  United  States  in   1922. 

Plant  Disease  Reporter,  Supplement  30,  1923. 

103.  WALLACE,  F.  N.    The  dormant  or  winter  spray.     State  Entomologist  of  Ind. 

Ann.  Rpt.  1915-16,  53-55.    1916. 

104.  WALTON,  R.  C.   Apple  blotch.    Ohio  State  Hort.  Soc.,  Ann.  Rpt.  1918.  48-51. 

105.    and  ORTON,  C.  R.     Time  of  apple  blotch  infection  for  1922  in 

southern  Pennsylvania.    Phytopath.  13,  43-44.     1923. 

106.  WATKINS,  O.  S.     Spraying — new  methods,  materials,  and  ideas.-    Trans.  111. 

State  Hort.  Soc.,  n.s.  46,  76-85.     1912. 

107. Conclusions  and  recommendations  from  spraying  experiments  in 

recent  years.     Trans.  111.  State  Hort.  Soc.,  n.s.  46,  395-408.     1912. 


70 


AUTHOR  INDEX 


559 


AUTHOR  INDEX 


Bakluf,  W.  V.,  and  Flint,  W.  P. 
Calcium  Cyanide  for  Chinch- 
Bug  Control 71-86 

Boughton,  I.  B.,  and  Graham, 
Robert.  Clostridium  botuli- 
num  Type  C :  A  Pathogenic 
Anaerobe  Associated  with  a 
Limberneck-Like  Disease  in 
Chickens  and  Ducks 1-34 

Burlison,  W.  L.,  Holbert,  James 
B.,  Koehler,  Benjamin,  Wood- 
worth,  C.  M.,  Dungan,  George 
H.  Corn  Boot,  Stalk,  and 
Ear  Bot  Diseases,  and  Their 
Control  Thru  Seed  Selection 
and  Breeding 235-478 

Case,  H.  C.  M.,  and  Mosher, 
M.  L.  Increasing  Farm 
Earnings  by  the  Use  of 
Simple  Farm  Accounts . . .  147-82 

Crandall,  Charles  S.  Blooming 

Periods  of  Apples 111-46 

Dungan,  George  H.,  Holbert, 
James  B.,  Burlison,  W.  L., 
Koehler,  Benjamin,  Wood- 
worth,  C.  M.  Corn  Boot, 
Stalk,  and  Ear  Bot  Diseases, 
and  Their  Control  Thru  Seed 
Selection  and  Breeding.  .235-478 

Graham,  Bobert,  and  Boughton, 
I.  B.  Clostridium  Botulinum 
Type  C:  A  Pathogenic  Ana- 
eroOe  Associated  with  a 
Limberneck-Like  Disease  in 
Chickens  and  Ducks 1-34 

Guba,  Emil  Frederick.  Phyllos- 
ticta  Leaf  Spot,  Fruit  Blotch, 
and  Canker  of  the  Apple: 
Its  Etiology  and  Con- 
trol  479-558 

Flint,  W.  P.,  and  Balduf,  W.  V. 
Calcium  Cyanide  for  Chinch- 
Bug  Control 71-86 

Harding,  H.  A.,  and  Prucha, 
M.  J.  Elimination  of  Germs 
from  Dairy  Utensils:  III. 
Steaming  Cans  Over  a 
Jet 227-34 

Holbert,  James  B.,  Burlison, 
W.  L.,  Koehler,  Benjamin, 
Woodworth,  C.  M.,  Dungan, 
Georgo  H.  Corn  Boot,  Stalk, 


PAGE 

and  Ear  Eot  Diseases,  and 
Their  Control  Thru  Seed  Se- 
lection and  Breeding 235-478 

Koehler,  Benjamin,  Holbert, 
James  B.,  Burlison,  W.  L., 
Woodworth,  C.  M.,  Dungan, 
George  H.  Corn  Boot,  Stalk, 
and  Ear  Bot  Diseases,  and 
Their  Control  Thru  Seed 
Selection  and  Breeding.  .235-478 

Mitchell,  H.  H.,  and  Bice,  John 
B.  The  Value  of  Mineral 
Supplements  in  Swine  Feed- 
ing   87-110 

Mosher,  M.  L.,  and  Case,  H.  C.  M. 
Increasing  Farm  Earnings  by 
the  Use  of  Simple  Farm 
Accounts 147-82 

Nevens,  W.  B.  The  Sunflower  as 
a  Silage  Crop :  Feeding 
Value  for  Dairy  Cows ;  Com- 
position and  Digestibility 
When  Ensiled  at  Different 
Stages  of  Maturity 183-226 

Overman,  O.  B.,  and  Tracy,  P.  H. 
A  Modification  of  the  Bab- 
cock  Test-  for  the  Determi- 
nation of  Fat  in  Butter- 
milk   63-70 

Prucha,  M.  J.,  and  Harding, 
H.  A.  Elimination  of  Germs 
from  Dairy  Utensils:  III. 
Steaming  Cans  Over  a 
Jet 227-34 

Bice,  John  B.  Feeding  Pigs  on 

Pasture 35-62 

Bice,  John  B.,  and  Mitchell,  H.  H. 
The  Value  of  Mineral  Sup- 
plements in  Swine  Breed- 
ing  87-110 

Tracy,  P.  H.,  and  Overman,  O.  B. 
.  A  Modification  of  the  Bab- 
cock  Test  for  the  Determina- 
tion of  Fat  in  Buttermilk . .  63-70 

Woodworth,  C.  M.,  Holbert, 
James  B.,  Burlison,  W.  L., 
Koehler,  Benjamin,  Dungan, 
George  H.  Corn  Boot,  Stalk, 
and  Ear  Bot  Diseases,  and 
Their  Control  Thru  Seed  Se- 
lection and  Breeding 235-478 


INDEX 


561 


INDEX 


(The  headings  in  capitals  are  subjects  of  entire  bulletins') 


PAGE 
Accounts,  see  Farm  accounts  and 

Farm  earnings 
Alfalfa    pasture,    Feeding    pigs 

on 43-47,  50-59 

Aplanobacter  stewarti   (E.  F.  S.) 

McCul 272-74,  421,  434-^3 

Apple  bitter  rot,  see  Apple  blotch 

Apple  blotch 479-557 

Bibliography 554-57 

Control  measures 

methods    previously    advo- 
cated   530-35 

protective     and     preventive 

measures 551-52 

pruning 550,  552-53 

recommendations 552-54 

selection     of     resistant     va- 
rieties   552,  554 

soil  treatments 550,  554 

spraying     experiments,     dor- 
mant   535-41 

effect  of  fungicide 539-41 

spraying    experiments,    sum- 
mer   541-50 

conclusions 548-50 

surgery 551 

Dissemination 528-30 

Distribution  and  prevalence  in 

Illinois 485-87 

History  of 481-84 

Life  history 505-26 

development  of  fungus. . .  .519-26 
inoculation  and  infection . .  505-06 

natural  infection 517-19 

sources  of  inoculum 506-07 

time  of  infection 507-17 

Morphology 488-92 

conidiophores 491 

mycelium 491-92 

pycnidia 488-90 

pycnospores 490-91 

Nomenclature 492-94 

Origin 484-85 

Physiology 494-504 

cultural  characters 494-96 

growth     and     pycnosclerotia 

formation 496-98 

spore  germination 500-04 

spore      production     in      cul- 
ture   498-500 

Plants  affected  by 487 

Varietal  susceptibility 526-28 


PAGE 

Apple  scab,  see  Apple  blotch 
Apples,  Blooming  periods  of.  .111-45 
Records  at  111.  Sta.  .113-16,  120-43 

amount  of  bloom 131-39 

amount  of  bloom  and  distri- 
bution    of    varieties     into 

time-groups 139 

blooming  period  of  1910.  .124-26 

character  of  records 114-15 

comparison     of     periods     of 

1904  and  1910 126-29 

early  blooming  varieties.  .122-23 
full  flowering  records  for  all 

varieties 120-22 

late  blooming  varieties 123-24 

summary 144-45 

temperature  and  distribution 

of  bloom 140-41 

variation  in  varietal  blooming 

periods 141-43 

varietal  flowering  periods. .  130-31 
Records  of  other  localities.  .116-20 

England 118-20 

New  York 116-17 

Oregon 118 

Virginia 116 

Variability    in    flowering    per- 
iod   115-16 

Ascaridia  perspicilli  in  chicken..       5 

Aspergillus  flamts  Link 271 

Aspergillus  niger 271 

Asperqillus  spp 271-72 

BABCOCK  TEST,  A  MODIFI- 
CATION OF  FOR  THE  DE- 
TERMINATION OF  FAT  IN 

BUTTERMILK 63-70 

Conditions  limiting  use  of.  ..66-68 
Comparison  with  normal  Butyl 

alcohol  method 68-69 

Comparison  with  Roese-Gottlieb 

method 68-69 

Conclusions 70 

Directions  for  operating 70 

Bacteria  in  milk  cans,  see  Milk 

cans 
Bacterial  wilt,  see  Aplanobacter 

stewarti 

Black  scab,  see  Apple  blotch 
Black -bundle  disease,  see  Cephal- 

osporium  a-cremonium 
BLOOMING  PERIODS  OF  AP- 
PLES, see  Apples 


562 


INDEX 


PAGE 

Blue      grass,      Feeding      pigs 

on 40-42,  59-60,  100-05 

Botulinus,  see  Clostridium  botuli- 

nus,  Type  C 
Buttermilk,  Determination  of  fat 

in,  see  Babcock  test 
Butyl    alcohol    method    compared 

with  Babcock  test 68-69 

CALCIUM  CYANIDE  FOB 
CHINCH-BUG  CONTROL... 71-84 

Care  in  handling 84 

Forms  used 74 

Methods  of  using 74-77 

alone  as  a  barrier 81-84 

in  strips  at  right  angles  to 
creosote  or  coal-tar  bar- 
rier   74-76 

on  trap  crops 79-81 

with  creosote  or  coal-tar  bar- 

iers 76-77 

Summary  of   experiments 72 

Calcium  gain  in  pigs  on  corn  and 

supplementary  feed 92 

Cancer,  see  Apple  blotch 

Capital    invested    in    farming    in 

Illinois 149 

Cephalosporium    acremonium 

Corda 267,  269-71, 

292,    351,    353,    359,    360,    383-84, 
391,    406,   421-24,    426-27,    432-43 
see  also  Corn  rot  diseases 
Chickens,  limberneck-like   disease 
in,   see    Clostridium    botuUnum 
type  C 
Chinch-bug  control 

Coal-tar  barrier  for 78-79 

Creosote  barrier  for 77-78 

Trap   crops  for 77-78 

see  also  Calcium  cyanide  for 

Chlorida  obsoleta 271 

Clostridium    botulinum    types    A 

and  B 3-4,  6,  8,  17,  33 

CLOSTRIDIUM  BOTULINUM 
TYPE  C:  A  Pathogenic  An- 
aerobe Associated  with  a  Lim- 
berneck-Like  Disease  in  Chick- 
ens and  Ducks 1-34 

Antitoxin 28-31 

Cultural  characters  differentia- 
ting types  A  and  B  from  C 
and  Parabotulinus  of  Sed- 

don 12 

Cultures  of  (plates) 9-10 

In  horses  and  cattle 28-29 

Presence  in  soil..  12,  23,  28,  29,  34 
Specimens     2770,     2771,    and 

2772 5-7 

Speciments  3419  and  3420 8-15 

bacteriologic   examination ...       8 
cultural  characters  in  various 
media 8-12,  13-15 


PAGE 

gross  pathology 8 

history 8 

Specimens     3421,   3422,     and 

3423 ..16-23 

bacteriologic   examination...      17 

clinical  symptoms 16 

gross  pathology 16-17 

history 16 

pathogenesis 17-23 

Specimens     3466,    3467,    and 

3468 23-28 

Summary 32-34 

Toxin  in  shelled  corn 31-32 

Corn 

Boil  smut  of,  see  Ustilago  seae 
Brown  smut  of,  see  Physoderma 

zeae-maydis 
Downy  mildew  of,  see  Scleros- 

pora  spp, ' 
Ear  characters  of  as  related  to 

yield,  literature  on 240-43 

Feeding  with,  see  Pigs  on  pas- 
ture, Feeding;  also  Swine 
feeding,  Value  of  mineral 
supplements  in 

Germinator  for  testing 357-58 

Head    smut    of,   see   Sphacelo- 

theca  reiliana 
Improvement     of,     Program 

of 447-69 

pure-line  method 455-68 

probable  uses  of  methods . .  468—69 

selection  method 448-55 

Mosaic  disease  of 282 

Purple-leaf  sheath  disease  of..  282 
CORN     ROOT,     STALK,    AND 
EAR   ROT   DISEASES,   AND 
THEIR     CONTROL     THRU 
SEED    SELECTION    AND 

BREEDING 235-478 

Corn  rot  diseases 

Bibliography 472-78 

Economic  importance  of ....  346—53 

estimate  of  losses 239,  353 

experiments  to  determine  loss 

thru  infected  seed 346-53 

Cephalosporium   infected.  .   351 

Diplodia-infected 347 

Fusarium-inf  ected 347-51 

scutellum  rotted 346-47 

extent    of    infection    on    111. 

farms 353 

Environmental  factors  affect- 
ing   283-328 

crop  sequence 323-28 

injurious  constituents  in  soil 

solution 319-23 

effect   of   limestone   appli- 
cations   319-23 

plant-food  materials   in   soil 
solution 309-18 


INDEX 


563 


PAGE 

soil  aeration 307-09 

soft  moisture 304-07 

soil  temperature  and  time  of 

planting 283-303 

Experimental    conditions    and 

methods 354—66 

experimental  plots 354—56 

germination   and   selec- 
tion   357-60 

harvesting  methods 362-63 

planting   and   cultural   meth- 
ods  360-62 

statistical  analysis 363-66 

strains  of  corn  used 356-57 

Genetic  factors  affecting. . .  .328-45 
differences     in     root     sys- 
tems   329-39 

Parasitic  factors  of 245-82 

bacterial  wilt 272-74 

black-bundle  disease 269-71 

corn  rust  and  other  diseases.  .   282 

corn  smut 279-81 

Diplodia 251-64 

Fusarium 265-68 

Gibberella 274-79 

miscellaneous    ear    rots    and 

molds 271-72 

miscellaneous   soil-borne   dis- 
eases   281 

Summary 470-71 

Susceptibility     and     resistance 

to 393-446 

differences     i  n     commercial 

strains 406-11 

influence  of  endosperm. .  .403-06 
influence  of  parent  plants.  .   393 
physical    characters    associa- 
ted with 411-30 

value  of  physical  appearance 

in  selection 431-46 

limitation     of     physical     se- 
lection   443-46 

Corn  rust,  see  Puccinia  sorghi 
Corn,  Seed  ears  of 

Performance     of      germinator- 

selected 366-67 

Physical  appearance  of  germi- 

nator-selected 368 

Physical  characters  associated 
with  infection  and  non- 
infection  366-92 

Relation  of  appearance  to  con- 
dition   368-82 

ear-tip  covering 371-73 

general  discussion 376-82 

kernel  indentation 373 

luster  of  ear 369 

luster  of  kernel 376 

nature  of  endosperm 373-75, 

Plate  IV  between  pp.  372-373 


PAGE 

shank  attachment 369-71, 

Plate  IV  between  pp.  372-373 
Value  of  single  ear  characters 

in  seed  selection 382-92 

coloring  of  cob  interior.  .384— 85, 
Plate   V  between  pp.   378-379 

luster  of  kernel 389-92 

nature  of  endosperm 

386-89,  390,  392 

shank  attachment 382-86 

Corn,     Self-fertilization     of,     see 

Improvement,  Program  of 
Corn     silage    vs.     sunflower    sil- 
age   185-87,  190-91, 

193-98,  204,  206,  208-10,  213,  215 
Corn  smut,  see  Ustilago  zeae 
Crop    acres    worked    per    horse. 

Effect  on  earnings 165-67 

Crop     acres     worked     per     man, 

Effect  on  earnings 163-64 

Crop  rotation,  Effect  on  corn  rot 

diseases 323-28 

Crop    yields,   Effect   on   earnings 

of  good  and  poor 157-60 

Dairy    cows,    Feeding    value    of 

sunflower  silage  for 183-225 

DAIEY  UTENSILS,  ELIMINA- 
TION OF  GERMS  FROM :  III 
Steaming  cans  over  a  jet... 227-34 

Bibliography 234 

Diplodia   root    rot,    see    Diplodia, 

zeae 

Diplodia  zeae  (Schw.)  Lev. . .  .251-64, 
265,    267,    272,    286,    287,    291-93, 
296-302, 305-07, 314-16, 318, 320-23, 
347,    358,    359-60,    361,    369,    371, 
373,  374,  377,  379,  381,  382,  384-86, 
391,   396,   401,   405,   415,   421,   470 
see  also  Corn  rot  diseases 
Dry  rot,  see  Apple  blotch 
Ducks,     Limberneck-like     disease 
in,   see   Clostridium   botulinum 
type  C 

ELIMINATION  OF  GERMS 
FROM  DAIRY  UTENSILS, 
III.  Steaming  Cans  Over  a 

Jet 227-34 

FARM  ACCOUNTS,  INCREAS- 
ING FARM  EARNINGS  BY 

THE  USE  OF  SIMPLE 147-82 

Benefits    realized    from    keep- 
ing   152-55 

Summary  of  study  of 148 

Woodford   county's  method  of 

conducting  work  on 151 

summary  of  records  kept  in 

(tables) 174-81 

Farm  earnings 

Effect  on  of  crop  yields. ..  .157-60 


564 


INDEX 


PAGE 
Effect  on  of  farm  organization 

and  management 155-57 

Effect     on     of     use     of     live- 
stock   160-63 

Effect  on  of  crop  acres  worked 

per  horse 165-67 

Effect  on  of  crop  acres  worked 

per  man 163—64 

Importance  of  thrift 167-69 

Increase   of   on   well   balanced 

farms 169-73 

see  also  Farm  accounts 

Farm   organization  and  manage- 
ment 

Effect     of     on     farm     earn- 
ings   155-57 

Measuring  success  of  farm ....   182 
Profit     in     well     balanced 
farms  .  . 169-73 

Farming,     Capital     invested     in 
Illinois 149 

FEEDING      PIGS      ON      PAS- 
TURE . 35-60 

Frog-eye  apple  leaf  spot 482 

Fruit  blotch,  see  Apple  blotch 

Field    peas    and    oats,    Feeding 
pigs  on 43,  45-47,  59 

Fusarium  moniliforme  Sheldon. . 
265-68,  272,  291,  294,  308,  311, 
312,  314,  316-17,  318,  347-51,  359, 
3J60,  369,  374,  376-79,  381,  382, 
385-86,  391,  396,  401,  415,  421 
Plate  I  between  pp.  250  and  251 
see  also  Corn  rot  diseases 

Fusarium  root   and   ear  rot,  see 
Fusarium  moniliforme 

Fusarium  spp 265, 

267,        271,         373,        379,        406 

Germs  in  milk  cans,  see  Milk  cans 

Gibberella     root     and     seedling 
blight,  see  Gibberella  saubinetti 

Gibberella      saubinetti      (Mont.) 

Sacc 243,  267, 

274-79,  284,  329-30,  339,  343,  393, 
396,  397,  399,  404-05,  421,  422, 
423,  424-26,  432-33,  434-43,  470 

Helminthosporium 281 

Hogs,  see  Swine 

lodids  for  farm  stock. . 89-90,  95 

Late  scab,  see  Apple  blotch 

Limberneck,  see  Clostridium   bo- 
tulinum 

Limestone,  influence  on  corn  rot 
diseases 319-23 

Livestock,  Effect  on  earnings  of 
use  of 160-63 

Milk  cans 

Safe    number     of     bacteria 
in.,  ..232-33 


PAGE 
Study  of  elimination  of  germs 

from 228-34 

bacterial  count  of  steamed. 231-32 
bacterial    count    of    un- 

steamed 230-31 

methods  of  study 228-30 

Time   and  steam   pressure  for 
sterilizing  ...  ...  .228-30,  233-34 

Mineral  requirements  of  ani- 
mals   89-90 

Mineral  supplements  in  swine 
feeding,  see  Swine  feeding 

Parabotulinus  organism 

4,  29-30,  32-33 

Pasteurella  avium 17 

Pasture  crops  for  pigs, 
Comparative  value  of  var- 
ious   38,  45,  51-52,  53,  55,  57 

One  vs.  two . '. 57-59 

Penicillum  spp 271-72 

Phyllosticta,  see  Apple  blotch 
PHYLLOSTICTA  LEAF  SPOT, 
FEUIT      BLOTCH,      AND 
CANKER   OF   THE   APPLE: 
Its  Etiology  and  Control.  .479-557 
Phyllosticta  solitaria,   see  Apple 

blotch 

Phyllostictose,  see  Apple  blotch 
Physoderma  zeae-maydis  Shaw..  282 
Pigs 

Carrying   fall    pigs   thru   sum- 
mer on  pasture 59-60 

Feeding  on  dry  lot... 50-52,  54-56 
Feeding  on  pasture 

comparative  value  of  various 

pasture  crops  

38,  45,   51-52,  53,  55,  57 

corn,    different    amounts,    with 

middlings  and  tankage .  .48-50 
corn,  different  amounts,  with 

tankage 43-47 

corn,    medium    rations,   with 

and  without  tankage ....  40-42 
corn    and    tankage    in    self- 
feeder  50-57 

without  concentrates .  43,  47,  48-49 
one  vs.  two  pasture  crops.. 57-59 

plan  of  experiment 39-40 

purpose  of  experiment 39 

summary 37-38 

see  also  Swine 

Pseudomonas  dissolvens 273 

Pseudomona-s  spp 273 

Puccinia  sorghi  Schw 282 

Pyrus  coronaria 485 

Rape,  Feeding  pigs  on.  .40-60,  98-100 
Red  clover  pasture,  Feeding  pigs 

on 52-54 

Ehizopus  spp 245,  246,  393 


INDEX 


565 


PAGE 

Eoese-Gottlieb  method  compared 
with  Babcock  method 68-60 

Sclerospora  spp 282 

Scutellum  rot 245-50, 

286,  291-94,  297,  299-302,  311, 
314-15,  318,  323-27,  346-49,  359, 
360,  369,  374,  377,  380,  382, 
383,  391,  396,  401,  402,  415,  420 
Plate  I  between  pp.  250  and  251 
see  also  Corn  rot  diseases 

Self -feeder,  used  for  minerals.  .98-106 
Used  with  pigs  on  pasture. .  .48-57 

Soybean  pasture,  Feeding  pigs 
on 43,  45-47 

Spacelotheca  reiliana  (Kiihn) 
Clinton 281 

Star  fungus,  see  Apple  blotch 

Statistical  analysis  used  in  corn 
experiments 363-66 

Stewart's  disease,  see  Aplano- 
bacter  stewarti 

SUNFLOWER  AS  A  SILAGE 
CROP:  Feeding  Value  for 
Dairy  Cows;  Composition  and 
Digestibility  When  Ensiled  at 
Different  Stages  of  Ma- 
turity   183-225 

Aero    yield    of    digestible    nu- 
trients   210,  215 

Bibliography 216-17 

Composition  of 203-10,  215 

Digestion  trial  of  at  different 

stages 211-13,  215,  221-25 

Effect     upon     composition     of 

milk 213-14 

Effect  upon  flavor  of  milk 214 

Growing  and  ensiling 188 

Plan  of  feeding  trial 189-93 

Results  of  feeding  trial 193-202 

detailed  data  (tables) 217-21 

economy  of  milk  and  fat  pro- 
duction. .193,  196-98,  200,  214 

gain  or  loss  in  weight 

193-98.  199,  201 


PAGE 

general  discussion 200-02 

milk  and  fat  production .... 

193,  194-95 

palatability.  .198-99,  200-01,  214 

physiological  effects .  199-200,  214 

Review  of  previous  work. .  .185-87 

Summary 214-15 

Sweet-clover  pasture,  Feeding 

pigs  on 40-42,  54-55 

SWINE  FEEDING,  VALUE  OF 
MINERAL  SUPPLEMENTS 

IN 87-110 

Economic     value     of     mineral 

feeding 96-97 

Experiments 97-109 

conclusions 110 

for    pregnant    and   lactating 

sows 106-09 

in    self-feeder    to    pigs    on 

pasture 100-02 

with  corn,  linseed  oil  meal, 
and  middlings  with  blue- 
grass  pasture 102-05 

with  corn,  middlings,  and 
tankage  with  and  without 

rape  pasture 98-100 

Improving  calcium  retention  on 

grain  rations 91-92 

Improving  quality  of  bone  on 

grain  rations 92-93 

Mineral  mixtures  —  homemade 

and  commercial 95-96 

Mineral  problem  in 91 

Review    of    experiments    at 

other  stations 93-95 

Value  of  different  minerals  as 

supplements 93-95 

Tar  blotch,  see  Apple  blotch 
Vstilago  zeae  (Beckm.)  Ung.. 279-81 
Woodford  county 

Study  of  farm  accounts  in . .  147-82 

Type  of  farming  in 150-51 

Seed  corn  from 406-11 

see  also  Farm  accounts 


THE  LIBRARY  OF  THE 
OCT  2  I  1931 

UNIVERSITY  OF  ILLINOIS, 


UNIVERSITY  OF  ILLINOIS-URBANA 


